JP3325806B2 - Water absorbing agent and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a water absorbing agent and a method for producing the same. More specifically, the present invention relates to a water-absorbing agent which is suitably used for sanitary materials such as disposable diapers (disposable diapers) and sanitary napkins, and which can significantly improve the water-absorbing ability of the above-mentioned sanitary materials, and a method for producing the same. is there.

[0002]

2. Description of the Related Art In recent years, water-absorbing agents such as water-absorbing resins have been widely used as one of materials constituting sanitary materials such as disposable diapers, sanitary napkins and incontinence pads for the purpose of absorbing a large amount of water. ing. In addition to the sanitary materials, a water absorbing agent such as a water absorbing resin has been widely used for the purpose of absorbing and retaining water, such as a soil water retaining agent and a drip sheet for food and the like.

Examples of the water-absorbing resin include a crosslinked product of a partially neutralized polyacrylic acid, a hydrolyzate of a starch-acrylonitrile copolymer, a neutralized product of a starch-acrylic acid graft polymer, and vinyl acetate-acrylic acid. Saponified acid ester copolymer, hydrolyzate of acrylonitrile copolymer or acrylamide copolymer or cross-linked thereof,
Crosslinked products of cationic monomers and the like are known.

For example, in order to be used as the above-mentioned sanitary materials, it is desired that the above-mentioned water-absorbing resin has the following characteristics. The properties that the water-absorbent resin should have are: high absorption capacity and excellent water absorption rate when in contact with an aqueous liquid such as a body fluid, liquid permeability, gel strength of a swollen gel,
The suction force when sucking up water from a base material containing an aqueous liquid is exemplified.

However, the relationship between these properties does not always show a positive correlation. For example, a water-absorbent resin having a higher absorption capacity has lower physical properties such as liquid permeability, gel strength, and water absorption rate. Therefore, as a method of improving the various absorption characteristics of such a water-absorbent resin in a well-balanced manner, various methods of crosslinking the vicinity of the surface of the water-absorbent resin have been proposed.

Among the above methods, a method using a specific compound as a crosslinking agent includes, for example,
(a) a method using a polyhydric alcohol (JP-A-58-180233, JP-A-61-16903), (b) a polyhydric glycidyl compound, a polyhydric aziridine compound, a polyhydric amine compound, a polyhydric isocyanate Method using compound (JP-A-59-189103)
Japanese Patent Application Laid-Open No. Sho 52), (c) a method using glyoxal
-117393), and (d) a method using a polyvalent metal (Japanese Unexamined Patent Publication No.
1-136588, JP-A-61-257235, JP-A-62-257235
No. 7745), a method using (e) a silane coupling agent (JP-A-61-211305, JP-A-61-252212, JP-A-61-264006), and (f) an epoxy compound. A method using a hydroxy compound (JP-A-2-132103), a method using (g) an alkylene carbonate (DE-4).
No. 020780) is known.

As a method of uniformly dispersing a cross-linking agent on the surface of a water-absorbent resin at the time of a cross-linking reaction, uniform surface cross-linking is performed. Method (JP-A-60-163956, JP-A-60
JP-A-255814), (i) a method in which a dihydric alcohol is present (JP-A-1-292004), (j) a method in which an ether compound is present (JP-A-2-153903), and (k) a monohydric alcohol. A method in which an alkylene oxide adduct of an alcohol, an organic acid salt, a lactam and the like are present (European Patent No. 555692) is known.

However, although the above surface treatment method can certainly improve the balance of various absorption characteristics of the water-absorbing resin, it is still not enough. In other words, the water-absorbent resin obtained by the above-mentioned conventional method is a recent trend, which uses a large amount of the water-absorbent resin, and is required for the water-absorbent resin used for the absorbent in a thinned sanitary article. Considering the properties to be performed, it is the present situation that the properties have not yet reached a sufficient level.
For this reason, higher quality of the water absorbent resin is required.

[0009] The properties required for the water-absorbent resin in the absorbent containing the water-absorbent resin at a high concentration include not only a high absorption capacity in a non-pressurized state, but also a higher load than before. And excellent absorption characteristics such as absorption capacity under high pressure and liquid diffusivity. In addition, when an absorbent containing a high concentration of water-absorbent resin is worn for a long time, the amount of water-soluble components (mainly water-soluble polymer components) in the water-absorbent resin gradually elutes, and In some cases, a phenomenon of reducing the diffusibility of the aqueous liquid or increasing the return amount of the aqueous liquid occurs, and it is desired to further reduce the amount of the water-soluble component in the water-absorbent resin.

A typical method for producing a water-absorbent resin is as follows:
A method of polymerizing a monomer containing acrylic acid or the like as a main component that has been neutralized in advance, (II) Acrylic neutralized at a relatively low neutralization rate within a predetermined range even if neutralization is not performed or neutralization is performed There is known a method of polymerizing a monomer mainly containing an acid or the like, and then neutralizing the obtained hydrogel polymer as required. However, the above method (I) has a relatively large amount of water-soluble components, and when the water-absorbing agent is used in sanitary goods, it reduces the diffusibility of aqueous liquids such as body fluids and the amount of the aqueous liquid returned. May increase. For this reason,
As a method for producing a water-absorbent resin, the above method (II) is suitably used as a method for maintaining a high absorption capacity of a water-absorbent resin under no pressure and reducing a water-soluble component.

As the method (II), specifically, for example, (1) a hydrogel polymer obtained by polymerizing a monomer containing a free acid group such as carboxylic acid or the like contains an alkali metal-containing polymer. A method of adding a compound to neutralize at least 50 mol% of acid groups in the hydrogel polymer (US Pat. No. 4,654,039)
No.), (m) adding an alkali metal-containing compound to a hydrogel polymer obtained by polymerizing a monomer containing an acid group such as a carboxylic acid, and adding 50% of the acid groups in the hydrogel polymer. Mole% to 90
And (n) adding an alkali metal-containing compound to a hydrogel polymer obtained by polymerizing a monomer containing an acid group such as a carboxylic acid, and adding the alkali metal-containing compound to the hydrogel polymer. After neutralizing 50 mol% to 90 mol% of the acid groups in the union, a compound having at least two or more reactive groups capable of reacting with the acid groups and / or alkali metal bases of the hydrogel polymer is provided. A method of causing a cross-linking reaction (JP-A-1-103606), and a method of polymerizing a monomer component obtained by neutralizing (o) 10 mol% to 50 mol% of an acid group-containing monomer (JP-A-1-444)
No. 04, U.S. Pat. No. 4,985,514), (p) After adiabatic polymerization of acrylic acid using a specific amount of three specific polymerization initiators until the residual monomer amount becomes 1000 ppm or less,
The obtained polyacrylic acid has a neutralization ratio of 50 mol% to 10 mol%.
0 mol%, and then a specific amount of a crosslinking agent is added to the neutralized hydrogel polymer to crosslink the hydrogel polymer, followed by further drying and pulverization (particularly, Kaihei 3-
174414, U.S. Pat. No. 5,145,906) and the like.

[0012]

However, as a result of various studies conducted by the inventors of the present invention, as in the above method (II),
The water-absorbent resin obtained by polymerizing the acid group-containing monomer and then neutralizing the water-soluble component can reduce the water-soluble component, but the cross-linking effect is exhibited even if the surface cross-linking treatment is performed. It turned out to be difficult.

That is, specifically, when the method (II) is used, the load to be applied is low (for example, 20 g / cm ² ).
In this case, the absorption capacity under pressure was improved to a certain level, but the absorption capacity under high pressure (for example, 50 g / cm ² ) was hardly improved. Further, even if a water-absorbing agent having a high absorption capacity under high pressure is obtained, it is not easy to obtain the water-absorbing agent stably, as described in (II) above.
It is difficult to say that any of the above-mentioned methods can stably obtain a water-absorbing agent having a high absorption capacity under high pressure.

Therefore, a water absorbing agent which has a high absorption capacity not only under no pressure but also under a high pressure, and has a reduced amount of water-soluble components as compared with the conventional one, can be suitably used for a thin absorber. And a method capable of stably producing the water-absorbing agent.

As a result of various studies by the present inventors,
As described above, the water-absorbent resin obtained by polymerizing the acid group-containing monomer and then neutralizing the swelled gel by absorbing the aqueous liquid, when the pH of the swelled gel increases over time. It was also found to change. That is, when the water-absorbent resin is used for sanitary goods, there arises a problem of safety due to the remaining alkali used for neutralization and a problem that the pH of the sanitary goods is not stable. Therefore, as a water-absorbing agent that can be more suitably used for an absorbent body such as a sanitary article, the water-absorbing agent is excellent in the above-mentioned absorption characteristics, and has a small pH change with time when an aqueous liquid is absorbed by the water-absorbing agent to form a swollen gel. Agents are needed.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to increase the absorption capacity under no pressure and under high pressure, and to reduce the amount of water-soluble components. Another object of the present invention is to provide a water-absorbing agent having a small change in pH of the swollen gel. Another object of the present invention is that the absorption capacity under no pressure and under high pressure is high, and the amount of water-soluble components is reduced as compared with the conventional one.
An object of the present invention is to provide a method capable of stably producing a water-absorbing agent having a small change in pH of a swollen gel.

[0017]

Means for Solving the Problems The inventors of the present application have conducted intensive studies to achieve the above object, and as a result, a hydrogel obtained by polymerizing a monomer component containing an acid group-containing unsaturated monomer (salt). The water-soluble component can be reduced by a method of post-neutralizing the water-soluble polymer, and the polymer particles derived from the polymer obtained by post-neutralizing the hydrogel polymer in the post-neutralization step It has been found that by controlling the neutralization ratio of each of the above, the cross-linking treatment of the polymer particle surface is performed efficiently, and a water-absorbing agent having a high absorption capacity under no pressure and under high pressure can be stably obtained. . Further, the inventors of the present invention have proposed a water absorbing agent (an aggregate of water absorbing agent particles) obtained by the above method.
Is that the neutralization rate of the water-absorbing agent particles constituting the water-absorbing agent is highly controlled, is uniformly neutralized at the particle level, and the swelling gel formed by swelling the water-absorbing agent has a small pH change over time. I found

That is, a water-absorbing agent according to the first aspect of the present invention is a water-containing gel obtained by polymerizing a monomer component containing an acid group-containing unsaturated monomer (salt) in order to solve the above problems. A water-absorbing agent obtained by post-neutralizing the water-soluble polymer, comprising an aggregate of a plurality of surface-crosslinked water-absorbing agent particles, wherein the water-absorbing agent particles
Assuming that the average neutralization rate of the aggregate of the children is Z ₂ (mol%),
Serial contained in 200 grain in water-absorbing agent particles, the water-absorbing agent particles having a low neutralization ratio than neutralization ratio Z ₁ satisfying the following relationship Z _1> Z ₂ -20 (mole%)
The number of pups is 10 or less, and the absorption capacity of physiological saline under a load of 50 g / cm ² is 20 g / g or more.

According to a second aspect of the present invention, there is provided a water-absorbing agent comprising a plurality of surface-crosslinked water-absorbing agents.
Of the water-absorbing agent particles.
Murrell, equation Z ₁ below> Z ₂ -20 absorbing agent particles having a low neutralization ratio than neutralization ratio Z ₁ satisfying (mol%)
It is characterized in that the number of offspring is 1 or more and 10 or less .

According to a third aspect of the present invention, there is provided a water absorbing agent according to the first or second aspect, wherein the neutralization ratio Z ₁ exceeds 55 mol%.
It is characterized by a sum rate .

According to a fourth aspect of the present invention, there is provided a water-absorbing agent comprising an acid group-containing unsaturated monomer.
Hydrogel polymerization by polymerization of monomer components containing (salt)
Multiple surface-crosslinked water-absorbing agents obtained by post-neutralizing the body
A water absorbing agent comprising an aggregate of particles, wherein the water absorbing agent particles
Absorption with a neutralization rate of 30 mol% or less contained in 200 grains
Liquid agent particles and water-absorbing agent particles having a neutralization rate of 95 mol% or more
And the total number is 30 or less, and a load of 50 g / cm ²
The absorption capacity of the physiological saline under the weight is 20 g / g or more .

According to a fifth aspect of the present invention, there is provided a water absorbing agent comprising a plurality of surface-crosslinked water absorbing agents.
Of the water-absorbing agent particles.
Water-absorbing agent particles having a neutralization rate of 30 mol% or less,
Total number of water-absorbing agent particles having a neutralization rate of 95 mol% or more
However, it is characterized in that not less than 1 grain and not more than 30 grains .

According to a sixth aspect of the present invention, there is provided a water absorbing agent according to any one of the first to fifth aspects , in order to solve the above problems.
The water-absorbing agent according to the above, wherein the water-soluble component of the water-absorbing agent is 10
% By weight or less .

According to a seventh aspect of the present invention, there is provided a water absorbing agent according to any one of the first to sixth aspects , in order to solve the above problems.
In the water absorbing agent described in the above item, the water absorbing agent is
5 minutes after 100 times swelling gel formed by swelling 0 times
Of the 100-fold swollen gel after the passage and after the passage of 120 minutes
It is characterized in that the pH change amount is 0.2 or less .

The water absorbing agent according to the invention of claim 8 is
To solve the above-mentioned problem, any one of claims 1 to 7
In the water-absorbing agent according to the above, the hydrogel polymer is
Inside, has a cross-linked structure introduced by an internal cross-linking agent,
The internal crosslinking agent is a non-ester bond type internal crosslinking agent.
It is characterized by.

According to the above configuration, it is possible to stably provide a water-absorbing agent which has a high absorption capacity under no pressure and under high pressure, and has a reduced amount of water-soluble components as compared with the prior art. . Since the water-absorbing agent can effectively exhibit its water-absorbing ability even when used in a thin absorber containing the water-absorbing agent at a high concentration, a large amount of the water-absorbing agent is used, and the thickness is reduced. It can also be suitably used as an absorbent in hygiene articles.

Moreover, in the above water absorbing agent, the neutralization ratio of the water absorbing agent particles constituting the water absorbing agent is controlled, and the neutralization at the particle level is made uniform. For this reason, the alkaline substance and the acidic substance used for neutralization do not remain in the water absorbing agent, and the water absorbing agent absorbs the aqueous liquid to form a swollen gel. And it is safe to use as an absorbent in the sanitary article, and can be used for a long time.

The method for producing a water absorbing agent according to the invention of claim 9, wherein, in order to solve the above problems, acid group-containing unsaturated
Hydrous gel formed by polymerizing monomer components containing monomers (salts)
Post-neutralizing the polymer, and the post-neutralized hydrogel
Reacting the polymer with the functional group of the hydrogel polymer
Reacting with the resulting crosslinking agent to crosslink the surface.
A method for producing a liquid medicine, comprising:
In the step of summing, the above hydrogel polymer is post-neutralized.
After drying and pulverizing, assuming that the average neutralization rate of the aggregate of polymer particles as a water absorbing agent precursor is Z ₂ (mol%) , first neutralization index indicating the number of relation Z _1> Z ₂ -20 polymer particles having a low neutralization ratio than neutralization ratio Z ₁ satisfying (mol%) is, on so as to be 10 or less
It is characterized by performing neutralization after writing .

The method for producing a water absorbing agent according to the invention of claim 11, wherein, in order to solve the above problems, in the method according to claim 9 or 10, wherein the water-absorbing agent, said neutralizing factor Z
₁ is characterized by having a neutralization ratio exceeding 55 mol%.

The method for producing a water absorbing agent according to the invention of claim 12, wherein, in order to solve the above problems, acid group-containing unsaturated saturated
Water-containing gel obtained by polymerizing a monomer component containing a sum monomer (salt)
Post-neutralizing the polymer, and post-neutralized hydrogel
Reacts with the functional group of the hydrogel polymer.
Reacting with a cross-linking agent that can be
A method for producing a water-absorbing agent, comprising:
In the neutralizing step, the above hydrogel polymer is post-neutralized.
After drying and pulverization , the number of polymer particles having a neutralization rate of 30 mol% or less and the neutralization rate of 95 mol% or more contained in 200 polymer particles as a water absorbing agent precursor And a second neutralization index indicating the total number of polymer particles having a
It is characterized in that the post-neutralization is performed as described below.

According to a thirteenth aspect of the present invention, in order to solve the above-mentioned problems, in the method of the twelfth aspect of the present invention, the post-neutralization is performed using the second neutralization method. sum index is characterized by performing such a 20 or less.

The method for producing the water absorbing agent to the invention of claim 14, wherein, in order to solve the above problems, according to claim 9 to 1
The method of manufacturing a water absorbing agent according to any one of 3, above
It is characterized in that the unsaturated monomer (salt) containing an acid group is free acrylic acid.

The method for producing the water absorbing agent to the invention of claim 15, wherein, in order to solve the above problems, according to claim 9 to 1
The method of manufacturing a water absorbing agent according to any one of 4, above
After the neutralization, mixing the hydrogel polymer and the neutralizing agent
After that, it is characterized by being further performed by mixing an aqueous liquid .

The method for producing the water absorbing agent to the invention of claim 16, wherein, in order to solve the above problems, in the method according to claim 15, wherein the water-absorbing agent, said hydrogel polymer
The amount of the aqueous liquid used is from 5 parts by weight to 100 parts by weight based on 100 parts by weight.
It is characterized by being within the range of parts by weight .

[0035] According to the above manufacturing method, the polymer particles constituting the polymer obtained by the post-neutralization, i.e., the upper
After neutralizing the hydrogel polymer, dry and pulverize it.
By controlling the neutralization rate of the polymer particles as a water-absorbing agent precursor, the absorption capacity under no pressure and under high pressure is high, and the amount of water-soluble components is reduced as compared with the conventional case. At the same time, a water-absorbing agent having a small change in pH of the swollen gel can be stably provided. Further, when producing the above-mentioned water-absorbing agent, the conditions satisfying the provisions of the neutralization index according to the present invention are confirmed in advance, and neutralization is performed according to the conditions, whereby the above-described water-absorbing agent excellent in each water-absorbing property is obtained. Can be efficiently obtained in a shorter time.

A water-absorbent article according to the invention of claim 17
In order to solve the above problems, any one of claims 1 to 8
Or compounding the water-absorbing agent according to claim 1 with a fibrous material.
It is characterized by being obtained.

According to the above arrangement, the water absorbing agent and the pulp
The ratio of the water-absorbing agent to the total with the fibrous material is 50% by weight or less.
Even when used under high concentration conditions such as above,
Without causing capillary blockage in
Excellent absorption over a long period of time with low leakage
An aqueous article can be provided.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail. The hydrogel polymer used in the method for producing a water absorbing agent according to the present invention is a polymer obtained by polymerizing a monomer component containing an acid group-containing unsaturated monomer (salt). As the above hydrogel polymer, a hydrogel polymer using acrylic acid (salt) as an acid group-containing unsaturated monomer (salt) is preferable, and 0 mol% to 40 mol% is neutralized. More preferably, it is a hydrogel polymer obtained by polymerizing acrylic acid (salt), and 0 mol% of neutralized free acrylic acid, that is, hydrous polymer obtained by polymerizing unneutralized acrylic acid is used. Particularly preferred is a gel polymer.

The above-mentioned monomer component contains the above-mentioned acrylic acid (salt) as a main component, and if necessary, other monomers other than the above-mentioned acrylic acid (salt), that is, the above-mentioned acrylic acid (salt). And other monomers copolymerizable with the polymer. The other monomer is not particularly limited, but specifically, for example, methacrylic acid, maleic acid, fumaric acid, crotonic acid, sorbic acid, itaconic acid, cinnamic acid, (anhydrous) Maleic acid, β-acryloxypropionic acid, vinylsulfonic acid, allylsulfonic acid, vinyltoluenesulfonic acid, styrenesulfonic acid,
Unsaturation containing acid groups such as 2- (meth) acrylamide-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, and 2-hydroxyethyl (meth) acryloyl phosphate Monomers and their salts; acrylamide, methacrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene Nonionic unsaturated monomers containing a hydrophilic group other than acrylic acid, such as glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate, vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine, etc. Is mentioned. One of these other monomers may be used alone, or two or more of them may be used as a mixture. When these other unsaturated monomers are used, the ratio of the other unsaturated monomers in the monomer component may be set so as to be 50 mol% or less, preferably 30 mol% or less.

When obtaining the above hydrogel polymer, it is desirable to introduce a crosslinked structure into the interior using an internal crosslinking agent. The above-mentioned internal crosslinking agent is not particularly limited as long as it is a compound having a plurality of polymerizable unsaturated groups and / or reactive groups in one molecule. That is, the internal cross-linking agent may be a compound having a plurality of substituents in one molecule which copolymerize and / or react with the acrylic acid (salt). The hydrogel polymer may have a self-crosslinking structure in which a crosslinked structure is formed without using an internal crosslinking agent.

As the internal crosslinking agent, specifically, for example, N, N'-methylenebis (meth) acrylamide,
(Poly) ethylene glycol di (meth) acrylate,
(Poly) propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, trimethylolpropane di (meth) acrylate,
Glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide-modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, Triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether,
Ethylene glycol, polyethylene glycol, propylene glycol, glycerin, pentaerythritol,
Examples include ethylenediamine, polyethyleneimine, glycidyl (meth) acrylate, and the like, but are not particularly limited. One of these internal cross-linking agents may be used alone, or two or more of them may be used as a mixture. By using an internal cross-linking agent having a plurality of polymerizable unsaturated groups in one molecule among the internal cross-linking agents exemplified above, it is possible to further improve the absorption characteristics and the like of the obtained water absorbing agent.

As the above-mentioned internal cross-linking agent, an internal cross-linking agent having a plurality of polymerizable unsaturated groups in one molecule is suitably used. (Meth) acrylate-based cross-linking agents having ester bonds (such as (poly) ethylene glycol di (meth) acrylate and trimethylolpropane tri (meth) acrylate) may not have good results in the present invention, Preferably, a non-ester bond type internal crosslinking agent having a plurality of polymerizable unsaturated groups in one molecule is more preferably used in the present invention.

Examples of the non-ester bond type internal cross-linking agent include an internal cross-linking agent having a plurality of polymerizable functional groups selected from an allyl group, an amide ester group and a vinyl group in one molecule. Acetal such as tetraallyloxyethane; pentaerythritol tetraallyl ether, pentaerythritol triallyl ether, pentaerythritol diallyl ether;
Has two or more hydroxyl groups in one molecule such as trimethylolpropane triallyl ether, trimethylolpropane diallyl ether, ethylene glycol diallyl ether, diethylene glycol diallyl ether, triethylene glycol diallyl ether, monosaccharide, disaccharide, polysaccharide, and cellulose Ethers such as polyallyl ether derived from compounds; triallyl isocyanurate, triallyl cyanurate and the like. Also,
Examples of the amide-based crosslinking agent include N, N′-methylenebis (meth) acrylamide, N, N′-methylenebis (N-vinylalkylamide), and the like. Further, examples of the vinyl-based cross-linking agent include divinyl benzene and divinyl ether.

The amount of the internal crosslinking agent used depends on the type of the crosslinking agent and the desired crosslinking density.
It is preferably in the range of 0.005 mol% to 3 mol%, more preferably in the range of 0.01 mol% to 1.5 mol%, and more preferably in the range of 0.05 mol% to
Particularly preferred is a range of 1 mol%. If the amount of the internal cross-linking agent is less than 0.005 mol% or more than 3 mol%, there is a possibility that a water-absorbing agent having desired absorption properties may not be obtained.

When the crosslinked structure is introduced into the water-absorbing agent by using the internal crosslinking agent, the internal crosslinking agent is added to the reaction system during or after polymerization of the monomer component, or after polymerization and neutralization. What is necessary is just to add it.

In the above polymerization, starch, a derivative of starch, cellulose, a derivative of cellulose,
A hydrophilic polymer such as a crosslinked product of polyvinyl alcohol, polyacrylic acid (salt), and polyacrylic acid (salt); a chain transfer agent such as hypophosphorous acid (salt), thiols, and thiolic acids may be added. .

The method for polymerizing the above monomer components is not particularly limited, and for example, known methods such as aqueous solution polymerization, reverse phase suspension polymerization, bulk polymerization, and precipitation polymerization can be employed. Among them, the ease of controlling the polymerization reaction,
From the viewpoint of the performance of the obtained water-absorbing agent, a method of polymerizing the monomer component in an aqueous solution, that is, an aqueous solution polymerization and a reverse phase suspension polymerization are preferable. Also, when performing aqueous polymerization,
Static polymerization, which is substantially performed without stirring, may be performed, or stirring polymerization may be performed, or static polymerization and stirring polymerization may be used in combination. Incidentally, aqueous solution polymerization, reverse phase suspension polymerization is a conventionally known polymerization method, for example, U.S. Patent No. 4,076,663
No. 4,625,001, No. 4,769,427, No. 4,87
No. 3,299, No. 4,093,776, No. 4,367,323, No.
No. 4,446,261, No. 4,683,274, No. 4,721,647,
No. 5,380,808 and the like.

When the aqueous solution polymerization and the reverse phase suspension polymerization are employed as the above polymerization method, the concentration of the monomer component, that is, the ratio of the monomer component in the aqueous solution is not particularly limited. It is preferable that the concentration is not lower than the saturation concentration and not higher than the saturation concentration, and more preferably in the range of 15% by weight to 40% by weight. The reaction conditions such as the reaction temperature and the reaction time may be appropriately set according to the composition of the monomer component to be used, and are not particularly limited.
The polymerization is carried out in a temperature range from 110 ° C, preferably from 10 ° C to 90 ° C.

When the polymerization is started, for example, potassium persulfate, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide, 2,2′-azobis (2-amidinopropane) dihydrochloride, etc. A radical polymerization initiator or an active energy ray such as an ultraviolet ray or an electron beam can be used. When an oxidizing radical polymerization initiator is used, redox polymerization may be performed using a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, or L-ascorbic acid in combination. The amount of these polymerization initiators used is preferably in the range of 0.001 mol% to 2 mol%, more preferably in the range of 0.01 mol% to 0.5 mol%. The polymerization initiator may be dissolved or dispersed in a solvent such as water.

The polymer obtained by the above polymerization is generally a hydrogel polymer, depending on the concentration of the aqueous solution of the monomer component. In the present invention, the hydrogel polymer is further neutralized by a neutralizing agent.

The shape of the hydrogel polymer before neutralization may be a gel obtained by standing polymerization, for example, a sheet gel obtained by belt polymerization, or a gel obtained by a cylindrical polymerization vessel. It may be a cylindrical gel or a box-shaped gel obtained by a box-type polymerization vessel. The gel obtained after the polymerization (hydrogel polymer) may be finely divided, or may be a particulate gel having a large surface area by finely dividing the gel at the same time as the polymerization, or may be obtained by reverse phase suspension polymerization. It may be a spherical gel.

In the present application, post-neutralization refers to polymerization of a monomer component containing acrylic acid (salt) which is not neutralized or has a relatively low neutralization ratio within a predetermined range even after neutralization.
This shows that the obtained polymer is adjusted to a desired neutralization rate by neutralization, and in the present embodiment, 0 mol% to 40 mol%.
After polymerizing a monomer component containing acrylic acid (salt) having a neutralization ratio of mol%, the resulting hydrogel polymer is neutralized to neutralize the hydrogel polymer. This indicates that the neutralization ratio of the resulting polymer is preferably adjusted to a neutralization ratio exceeding 55 mol%. The above-mentioned neutralization ratio is the mol% of the acrylate in the total amount of the acrylic acid and the acrylate, and the monomer component containing the above-mentioned acrylic acid (salt) in terms of various physical properties, environment, and safety. It is preferable to adjust the neutralization ratio of the polymer obtained by neutralizing the hydrogel polymer obtained by polymerizing to a neutralization ratio of more than 55 mol%, from 55 mol% to 85 mol%. It is more preferable to adjust the neutralization rate to 65 mol% to 75 mol%, and it is particularly preferable to adjust the neutralization rate to 65 mol% to 75 mol%.
The neutralization rate of the polymer obtained by neutralizing the hydrogel polymer is the neutralization rate of the neutralized hydrogel polymer (neutralized gel) obtained by actual measurement or calculation. More specifically, the average neutralization rate of a plurality of polymer particles (aggregate of polymer particles) obtained by drying and pulverizing the above neutralized gel is shown. The desired neutralization rate of the polymer obtained by neutralizing the hydrogel polymer is equal to the desired neutralization rate of the obtained water-absorbing agent.

As a conventional method for producing a water-absorbing agent, there is also a method for obtaining a water-absorbing agent by polymerizing acrylic acid which has been neutralized in advance so as to have a desired neutralization ratio. However, the water-absorbing agent obtained by this method has a relatively high water-soluble component content, and when the water-absorbing agent is used in sanitary articles, it reduces the diffusibility of aqueous liquids such as body fluids, It is not preferable because there is a possibility that a phenomenon of increasing the return amount of the liquid may occur.

The water-absorbing agent of the present invention is derived from a polymer obtained by post-neutralizing a hydrogel polymer obtained by polymerizing a monomer component containing the above-mentioned unsaturated monomer (salt) containing an acid group. By controlling the neutralization rate of each polymer particle, it is possible to obtain easily and stably. Specifically, the water absorbing agent of the present invention,
The hydrogel polymer obtained by polymerizing a monomer component containing the acid group-containing unsaturated monomer (salt) is post-neutralized so that the neutralization index is equal to or less than a predetermined value. The obtained polymer can be easily and stably obtained by reacting the polymer with a crosslinking agent capable of reacting with a functional group of the polymer.

In the present invention, the neutralization index refers to the neutralized state of a polymer obtained by neutralizing a hydrogel polymer formed by polymerizing an acid group-containing monomer, This is a novel parameter represented by the number of particles having an unacceptable neutralization ratio contained in a predetermined amount of polymer particles obtained by pulverization. In the present embodiment, a polymer obtained by polymerizing a monomer component containing an acid group-containing monomer, preferably acrylic acid (salt), and undergoing a post-neutralization step reacts with a functional group of the polymer. The neutralization state of the polymer at the time of mixing and reacting with a crosslinkable agent, which is lower than the first allowable neutralization ratio contained in a predetermined amount of polymer particles obtained by drying and pulverizing the polymer. The neutralization index represented by the number of polymer particles having a neutralization ratio is 1st.
Of the neutralization index. Further, regarding the neutralized state of the polymer, the number of polymer particles having a lower neutralization rate than the second allowable neutralization rate contained in a predetermined amount of the polymer particles, and the second allowable neutralization rate The neutralization index indicated by the total number of polymer particles having a higher neutralization rate than the number of polymer particles having a higher neutralization rate is defined as a second neutralization index.

Hereinafter, the method of measuring the neutralization index of the present invention will be described.
This will be described below with reference to FIG. First, as shown in FIG. 2, on a lower surface side of a plastic plate 22 having a thickness of 1.6 mm provided with an opening 22a having a size of 20 mm × 20 mm, a size of 25 mm × 25 mm is covered so as to cover the opening 22a. Is attached with a transparent adhesive tape (not shown). Next, in the vicinity of the center of the opening 22a, the polymer particles 21 classified into 300 μm to 600 μm were placed.
Spray 200 tablets. Next, 0.2 ml of deionized water is added to the polymer particles 21 using a micro syringe.
Immediately before the polymer particles 21 swell and absorb deionized water, 0.05 ml of a 1.5: 1 mixed solution of a 0.1% ethanol solution of bromthymol blue (BTB) and a 0.1% ethanol solution of methyl red (MR) is micronized. Add using a syringe. Thereby, a colored swelling gel is obtained. Then, on the upper surface side of the plastic plate 22,
A cover glass 23 having a size of 25 mm × 25 mm is placed so as to cover the opening 22a.
The swollen gel is pushed and spread into the opening 22a covered with 23 '. Then, among the colored gel particles forming the swelling gel, the number of particles having a color corresponding to the color of the comparative particles is measured and defined as a neutralization index. The cover glass 23
23 ′ is transparent and the transparency of the gel particles is high, and since the gel particles are almost aligned in the opening 22a of the plastic plate 22, even if the gel particles partially overlap, Thus, all the gel particles can be confirmed from the upper and lower surfaces of the plastic plate 22.

As a method of neutralizing the above-mentioned hydrogel polymer, for example, a hydrogel polymer is finely divided in a vessel having a plurality of rotating shafts by a shearing force caused by rotation of the rotating shaft while a neutralizing agent or the like is used. A method of adding and kneading the aqueous solution (JP-A-1-131209) is known. However,
These methods are inadequate to achieve the neutralization index of the present invention.

Here, when the first neutralization index is adopted as the above-mentioned neutralization index, the comparative particles refer to a desired neutralization ratio (that is, an acid group-containing monomer, preferably acrylic acid ( salt)
The neutralization rate of the polymer obtained by neutralizing the hydrogel polymer obtained by polymerizing a monomer component containing, the polymer is an aggregate of polymer particles obtained by drying and grinding Average neutralization rate)
The particles classified into 300 μm to 600 μm obtained by drying each hydrogel polymer having a neutralization ratio lower by 20 mol% or more than the above are shown. The particles for comparison also include particles obtained by drying a hydrogel polymer before neutralization (that is, a hydrogel polymer having a neutralization ratio of 0 mol%). In this case, the particles having a color corresponding to the color of the comparative particles are defined as particles having a color corresponding to the color obtained when the above-described mixed indicator is added to the comparative particles. In other words, the color of the comparative particles means that when the hydrogel polymer having a neutralization ratio of 0 mol% is neutralized to a neutralization ratio of 75 mol%, each neutralization ratio is from 0 mol% to 55 mol%. This is the color of the particles when the above-mentioned mixed indicator is added to the particles obtained by drying each hydrogel polymer obtained by polymerizing each acrylic acid (salt) without post-neutralization.

In the present invention, the number of particles having a color corresponding to the color of the comparative particles is obtained by drying each hydrogel polymer having a neutralization ratio of at least 20 mol% lower than the desired neutralization ratio. It is preferably determined by measuring the number of particles having a color corresponding to the color obtained when the above-mentioned mixed indicator is added to the particles classified into 300 μm to 600 μm.

However, from the viewpoints of various physical properties, environmental properties and safety, the neutralization rate of the polymer obtained by neutralizing the hydrogel polymer used as a raw material of the water absorbing agent, that is, the polymer is dried, The average neutralization rate of a plurality of pulverized polymer particles (aggregate of polymer particles) can be adjusted to a neutralization rate exceeding 55 mol%, preferably from 65 mol% to 75 mol%. Preferably, and particularly, the neutralization rate of the polymer particles is 55 mol%
Can be obtained stably by controlling each of them so that the absorption capacity under high pressure is exceeded. Therefore, the measurement of the number of particles of a color corresponding to the color of the comparative particles is performed in a desired manner. Among the hydrogel polymers having a neutralization ratio of at least 20 mol% lower than the sum rate, in particular, particles obtained by drying each hydrogel polymer having a neutralization ratio of 55 mol% or less are obtained. Particles having a color corresponding to the color when the above-mentioned mixed indicator is added may be regarded as particles having a color corresponding to the color of the comparative particles. Further, as the comparative particles, particles of a crosslinked polyacrylic acid having the above neutralization ratio may be used instead of the hydrogel polymer having the above neutralization ratio.

According to the present invention, the number of polymer particles having a color corresponding to the color of the comparative particles contained in the aggregate of the polymer particles is measured, whereby the number of the polymer particles contained in the aggregate of the polymer particles is measured. The number of polymer particles having an unacceptable neutralization rate can be determined.

Further, as a result of further studies by the inventors of the present invention, when neutralizing the hydrogel polymer and then subjecting the resulting polymer to surface cross-linking, it has a neutralization ratio of 95 mol% or more. It was found that the presence of the Japanese product made it difficult to exhibit the surface treatment effect. In particular, when free alkali remains in the polymer, even if the remaining amount is small, the absorption capacity is expected to be lower than the remaining alkali amount or more, under high pressure. Absorption capacity is greatly reduced.

Further, according to the study by the present inventors, 55
Among the polymer particles having a neutralization ratio of not more than mol%, particularly, the presence of the polymer particles having a neutralization ratio of not more than 30 mol% greatly reduces the mixing property and the dissociation degree of the surface cross-linking agent. It was found that the abundance greatly hindered the improvement of the absorption capacity under high pressure than originally expected.

Therefore, in the present invention, the term “second allowable neutralization ratio” means that the neutralization ratio of the polymer particles exceeds 95% by mole.
And a neutralization index indicated by the total number of polymer particles having a neutralization ratio of 30 mol% or less and the number of polymer particles having a neutralization ratio of 95 mol% or more. Is the second neutralization index. According to the present invention, the neutralization ratio of the polymer particles is controlled so as to be more than 30 mol% and less than 95 mol%, respectively, so that the second neutralization index becomes a predetermined value or less. By neutralizing the hydrogel polymer, a water-absorbing agent having excellent absorption capacity under high pressure can be stably obtained.

When the second neutralization index is used as the neutralization index, the comparative particles are 300 μm obtained by drying each hydrogel polymer having each neutralization ratio of 30 mol% or less.
Particles obtained by drying the hydrogel polymer having a neutralization rate of 95 mol% or more, and particles classified to 600600 μm.
The particle | grains classified into 300 micrometers-600 micrometers are shown. And also when employ | adopting the said 2nd neutralization index, the particle of the polyacrylic acid crosslinked body which has said neutralization ratio can be substituted as said comparative particle.

In the measurement of the neutralization index, the color when the mixed indicator was added to the polymer particles 21 was as follows:
As the neutralization rate of the polymer particles 21 increases, the color becomes red →
It changes continuously from orange → yellow → yellow green → green.

Accordingly, as a simple method of measuring the first neutralization index, a method of measuring the number of particles having a color corresponding to the color of the comparative particles is as follows. Particles having the same color as the color obtained when the mixed indicator is added to particles obtained by drying a hydrogel polymer having a relative degree (or a crosslinked polyacrylic acid having a neutralization ratio of 55 mol%), What is necessary is just to count the number of particles reddish than the particles.

Similarly, as a method for simply measuring the second neutralization index, a water-containing gel having a neutralization ratio of 30 mol% is used for counting the number of particles having a color corresponding to the color of the comparative particles. Particles of the same color as those obtained by adding the above-mentioned mixed indicator to particles obtained by drying a polymer (or a crosslinked polyacrylic acid having a neutralization ratio of 30 mol%), and a reddish color more than the particles. The above mixed indicator was added to the particles obtained by drying the hydrogel polymer having a neutralization ratio of 95 mol% (or crosslinked polyacrylic acid having a neutralization ratio of 95 mol%). The number of particles having the same color as the color obtained in this case and the number of greenish particles may be measured.

When there is no particle of 300 μm to 600 μm in the sample, 150 μm to 300 μm or 6 μm
Evaluation can also be performed using particles of 00 μm to 850 μm.

As described above, in the present invention, the first allowable neutralization rate is defined as the average neutralization rate of the aggregate of the polymer particles, where Z ₁ (mol%) is the allowable neutralization rate of the polymer particles. The rate is Z ₂
(Mol%), the neutralization rate that satisfies the following relational expression Z ₁ > Z ₂ -20 (mol%) (that is, not less than 20 mol% or more than the average neutralization rate of the polymer particles) Sum rate) or a neutralization rate exceeding 55 mol%. The term "non-first allowable neutralization ratio" means that the neutralization ratio is at least 20 mol% lower than the average neutralization ratio of the polymer particles or 55 mol% or less.

In the present invention, the second allowable neutralization ratio means a neutralization ratio of more than 30 mol% and less than 95 mol%, and the non-second allowable neutralization ratio is 30 mol% or less. Indicates a neutralization rate or a neutralization rate of 95 mol% or more.

Specifically, the post-neutralization is performed so that the first neutralization index is 10 or less, and the post-neutralization is performed so that the second neutralization index is 30 or less. The former method is more preferable. For the above-mentioned reason, it is particularly preferable that the post-neutralization is performed so as to satisfy both the conditions relating to the neutralization index described in the above methods.

In the present invention, when the above method is employed, the number of polymer particles having a non-first neutralization ratio in 200 polymer particles is 10 or less (that is, the aggregate of polymer particles). If the ratio of the number of polymer particles having the first allowable neutralization ratio in the body is greater than 95% and the ratio of the number of polymer particles having the non-first neutralization ratio is 5% or less), It is possible to stably obtain a water-absorbing agent having an excellent absorption capacity under rolling. However, as described above, there is a problem that the presence of a highly neutralized substance having a neutralization ratio of 95 mol% or more makes it difficult to exhibit the surface treatment effect. Therefore, the total of the number of polymer particles having a non-first allowable neutralization ratio and the number of polymer particles having a neutralization ratio of 95 mol% or more in 200 polymer particles is 10%.
Or less (i.e., the proportion of the number of polymer particles having a neutralization ratio of more than 55 mol% and less than 95 mol% in the aggregate of polymer particles is greater than 95%, and the neutralization ratio of 55 mol% or less) Is less than or equal to 5%, or more than the average neutralization rate of the polymer particles in the aggregate of the polymer particles. The ratio of the number of polymer particles having a neutralization ratio of not less than 20 mol% and not less than 95 mol% is larger than 95%, and is lower than the average neutralization ratio of the polymer particles by 20 mol% or more. If the total ratio of the polymer particles having a sum rate and the number of polymer particles having a neutralization rate of 95 mol% or more is 5% or less),
In particular, a water-absorbing agent that is more excellent in absorption capacity under high pressure can be obtained more stably.

Further, according to the present invention, even when the first neutralization index exceeds 10, if the second neutralization index is 30 or less, the absorption characteristics, especially the high A water-absorbing agent having excellent absorption capacity under pressure can be obtained stably.

In the present invention, the first neutralization index is:
It is necessary to be 10 or less (that is, 0 or more and 10 or less), and preferably 5 or less. Further, the second neutralization index needs to be 30 or less (that is, 0 or more and 30 or less), and preferably 20 or less. The neutralization index of 0 means that there is no particle having a color corresponding to the color of the comparative particles in the method of measuring the neutralization index, that is, the desired neutralization ratio is completely and uniformly obtained at the polymer particle level. Indicates neutralized.

In the first production method, a polymer obtained by polymerizing a monomer component containing acrylic acid (salt) is provided;
The point at which the functional group of the polymer is reacted with a crosslinking agent capable of reacting is preferably neutralized by post-neutralizing the hydrogel polymer by the method of the present invention, and then dried and pulverized to obtain a water absorbing agent as a final product. After adjusting to a close particle size. Therefore, in this case, the first neutralization index of the polymer particles as the water-absorbing agent precursor, which has been adjusted to a particle size close to that of the final product by dry grinding, is 10 or less and / or the second neutralization index is 30 or less. What is necessary is just to neutralize the hydrogel polymer so that it may become.

Since the above neutralized state is maintained after the crosslinking reaction, the neutralization index of the water-absorbing agent as the final product is not changed during the crosslinking reaction unless the water-absorbing agent absorbs water to form a swollen gel. The neutralization index of the polymer particles is maintained. That is, the neutralization index of the polymer particles becomes the neutralization index of the water-absorbing agent as it is. The neutralization index of the water-absorbing agent as a final product can be measured by the same method as the neutralization index of polymer particles obtained by polymerizing a monomer component containing acrylic acid (salt).

Further, since the desired neutralization rate of the water absorbing agent is equal to the desired neutralization rate of the polymer particles, and the neutralization index of the polymer particles is maintained after the production of the water absorbing agent. In the present invention, the allowable neutralization ratio of the water-absorbing agent particles constituting the water-absorbing agent is equal to the allowable neutralization ratio of the polymer particles. Therefore, the first allowable neutralization rate of the water-absorbing agent particles means that the allowable neutralization rate of the water-absorbing agent particles is Z ₁ (mol%), and the average neutralization rate of the aggregate of the water-absorbing agent particles is Z ₂ ( %, The neutralization ratio satisfying the following relational expression Z ₁ > Z ₂ -20 (mol%) (that is, neutralization not less than 20 mol% or more than the average neutralization ratio of the water-absorbing agent particles). %) Or a neutralization rate of more than 55 mol%. In addition, the non-first allowable neutralization rate of the water-absorbing agent particles means that the neutralization rate is 20 mol% or less lower than the average neutralization rate of the water-absorbing agent particles or 55 mol% or less. Show. In the present invention, the second allowable neutralization ratio of the water-absorbing agent particles indicates a neutralization ratio of more than 30 mol% and less than 95 mol%, and the non-second allowable neutralization ratio is 30 mol% or less. , Or a neutralization rate of 95 mol% or more.

As described above, the neutralization index is determined by comparing particles of a color corresponding to the color of the comparative particles in the polymer particles 21 with:
That is, the number of particles (particles having a non-permissible neutralization ratio; hereinafter, referred to as non-neutralized particles) that deviate from the permissible neutralization ratio range, and how uniformly the polymer particles are neutralized one by one. Can be evaluated. The lower the neutralization index, the smaller the variation in pH among the polymer particles, the better the safety, and the stability of the water-absorbing agent with high absorption capacity under high pressure and high load, which is the object of the present invention. Can be obtained. In other words, the above neutralization index is such that the absorption capacity under no pressure and under high pressure is both high, and the amount of water-soluble components is lower than before and the safety is excellent. This is particularly important for stably obtaining a water-absorbing agent having a small change.

For example, the above-mentioned prior application discloses a water-absorbent resin obtained by neutralizing a hydrogel polymer obtained by polymerizing a monomer component containing acrylic acid (salt) and then crosslinking with a crosslinking agent. Has been described. However, in these documents, the polymer obtained by post-neutralization is dried and pulverized to adjust the particle size to a size close to that of a water-absorbing agent as a final product, and at the particle level of the polymer at the time of reacting with a surface crosslinking agent. No consideration is given to the uniformity of the neutralization state of the polymer particles, and even if the neutralization of the polymer surface is uniform, the polymer particles are usually dried and pulverized, and then polymer particles at the time of performing the surface crosslinking reaction The neutralization state of each grain is still uneven.

That is, conventionally, in the hydrogel polymer, a state in which the basic substance is not confirmed visually or by an indicator, specifically, even when phenolphthalein is added to the hydrogel polymer, The point in time at which coloration (red) due to phthalein was not confirmed was regarded as the end point of the neutralization of the hydrogel polymer. However, the above-mentioned hydrogel polymer, that is, the polymer obtained through the post-neutralization step, which is used as a raw material of the conventional water-absorbent resin, has a macroscopically desired neutralization ratio. However, when the polymer particles are evaluated at the micro level, not all of the polymer particles have a desired neutralization ratio.

In fact, when the uniformity of the neutralized state of the polymer obtained through the conventional post-neutralization step was evaluated by the first neutralization index of the present invention, the conventional polymer particles were compared with the present invention. As a result, as shown in FIG. 4, a large number of non-neutralized particles 21b are found in a mixture with particles (hereinafter, referred to as neutralized particles) 21a within the allowable neutralization ratio range.

The water-absorbing resin (water-absorbing agent) obtained by reacting the polymer having a large neutralization index with a crosslinking agent capable of reacting with the functional group of the polymer has an absorption property under a low pressure. Although the magnification is improved to a certain level, the absorption capacity under high pressure is hardly improved to a certain level. Moreover, the pH of the swelled gel formed by swelling the water-absorbent resin changes with time. Thus, in order to achieve the object of the present invention, in particular, to improve the absorption capacity under high pressure, the first neutralization index is 10 or less and / or the second neutralization index is 30 or less. Is critically essential. When the neutralization index exceeds the above value, the absorption capacity under no load (no pressure) or under low pressure does not change much. Due to the presence ratio of particles corresponding to the color (for example, 10 particles / 200 particles or 30 particles / 200 particles), the physical properties are greatly reduced more than the physical properties that are originally predicted to be reduced.

As a specific method for achieving the neutralization index of the present invention, for example, (1) a neutralizing agent is added to a hydrogel polymer, and the mixture is sufficiently stirred, and then an aqueous liquid is further added. Method for causing rearrangement in the wetting agent, (2) a hydrogel polymer,
A method of sufficiently immersing in a neutralizer solution containing a larger amount of neutralizer than the amount of neutralizer required to achieve the target degree of neutralization, followed by filtration, (3) Neutralizer 1 μm to 1000 μm
(4) a method of mixing with a hydrogel polymer over a long period of time under stirring and forming very fine droplets within the range of (4), adjusting the particle size of the hydrogel polymer to a range of 1 μm to 1000 μm rear,
A method of adding a neutralizing agent, (5) a method of allowing the hydrogel polymer to which the neutralizing agent has been added to be left under a high pressure state or a pressurized state, and (6) a method of adding a neutralizing agent to the hydrogel polymer. (7) a method of irradiating a microwave, an ultrasonic wave or the like, (7) a method of allowing a hydrogel polymer to which a neutralizing agent is added to be left for at least 24 hours (until the neutralization index of the present invention is achieved), (8) an interface In the presence of an activator or inorganic powder, a method of adding and mixing a neutralizing agent to the hydrogel polymer, (9) to the particulate hydrogel polymer obtained by reverse phase suspension polymerization, A method of directly spraying a neutralizer aqueous solution without passing through an organic solvent, (10) drying the hydrogel polymer,
A method of mixing a neutralizing agent aqueous solution with a powder having a particle size close to the water-absorbing agent as a final product obtained by pulverizing as necessary (water-absorbing agent precursor), (11) the powder (water-absorbing agent precursor),
After sufficiently immersing in a neutralizing solution containing a larger amount of neutralizing agent than the amount of neutralizing agent required to achieve the target degree of neutralization, a method of filtering, such as (12) ammonia A method of reacting a gaseous neutralizing agent with a hydrogel polymer is exemplified. Among them, the method (1) is particularly preferable because the neutralization index of the present invention can be achieved easily and in a short time, and a water absorbing agent having more excellent absorption performance can be obtained.

The neutralizing agent used to achieve the neutralization index of the present invention is not particularly limited, and conventionally known inorganic or organic salts or acids can be used. Specific examples of the neutralizing agent include sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide, sodium carbonate, potassium carbonate, ammonium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, and ammonium hydrogen carbonate. , Sodium phosphate,
Potassium phosphate, ammonium phosphate, sodium borate, potassium borate, ammonium borate, sodium acetate, potassium acetate, ammonium acetate, sodium lactate, potassium lactate, ammonium lactate, sodium propionate, potassium propionate, ammonium propionate, etc. Is mentioned.

These neutralizing agents may be used alone or in a combination of two or more. Among them, when the hydrogel polymer obtained by polymerizing a monomer component mainly composed of acrylic acid is post-neutralized, sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide Hydroxides of monovalent cations such as sodium carbonate, potassium carbonate, ammonium carbonate, sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, etc .; Moreover, it is preferable because it has high physical properties and can efficiently reduce the neutralization index.

A method for neutralizing a hydrogel polymer in a high pH region using an inorganic acid or an organic acid,
Even when a method of neutralizing with an acid after being made alkaline, a water-absorbing agent excellent in water absorption capacity under high pressure and high load can be obtained as long as the neutralization index falls within the range of the present application. Examples of the organic acid or inorganic acid used in this case include, for example, phosphoric acid, sulfuric acid, hydrochloric acid, carbonic acid, nitric acid,
Examples thereof include citric acid and lactic acid, but are not particularly limited. Also in this case, these organic acids and inorganic acids may be used alone or as a mixture of two or more.

These neutralizing agents can be added to the hydrogel polymer in the form of an aqueous solution; a slurry; powders such as powders and granules. Among them, it is preferable to use the neutralizing agent as an aqueous solution because the time required to reach the neutralization index can be shortened.

The aqueous liquid used in the above method (1) is preferably water, and water is used as a main component, and other salts other than bases and hydrophilic organic solvents are used for the purpose of the present invention. It may be included within a range that does not interfere.

When the aqueous solution is added during the neutralization of the hydrogel polymer, a neutralizing agent is added to the hydrogel polymer to neutralize the surface of the hydrogel polymer to a desired pH range. It is preferable to add the aqueous liquid after confirming that the operation has been performed. In this case, a neutralization indicator such as phenolphthalein is suitable for confirmation of neutralization.

The amount of the aqueous solution added is determined by the amount of the hydrogel polymer.
The amount is preferably from 2 to 100 parts by weight, more preferably from 5 to 100 parts by weight, particularly preferably from 10 to 50 parts by weight, per 100 parts by weight. If the added amount of the aqueous liquid is less than 2 parts by weight, the neutralization index is 10
The time required to reduce the amount below is too long.
On the other hand, if the amount of the aqueous liquid exceeds 100 parts by weight, the drying conditions become severe, and the drying step for obtaining the final product becomes too burdensome, which is not industrially preferable.

When the aqueous liquid is added, the aqueous liquid and the hydrogel polymer are preferably mixed or kneaded continuously or intermittently. In addition, it is preferable to keep the mixture for 1 hour or more, more preferably 2 hours or more, and particularly preferably 6 hours or more, until the neutralization is completed.
Hold for more than an hour, most preferably for more than 12 hours. The holding temperature in this case is in the range of 0 ° C to 80 ° C,
The conditions are preferably such that the water content of the hydrogel polymer does not change within the range of 5 ° C to 50 ° C. More preferably, the addition amount and the holding time of the aqueous liquid are selected such that the first neutralization index is 5 or less and / or the second neutralization index is 20 or less.

Thus, the polymer post-neutralized by the method of the present invention has a first neutralization index of 10 or less and / or a second neutralization index of 30 or less, as shown in FIG. In addition, the number of non-neutralized particles 21b is smaller than in the conventional case, and the particles are more uniformly neutralized at the particle level.

The water-absorbing agent according to the present invention can be obtained by reacting a polymer post-neutralized by the above-mentioned method with a crosslinking agent capable of reacting with a functional group of the polymer to form a surface cross-linking. . As described above, the polymer whose neutralization rate is controlled at the particle level is treated in the presence of the cross-linking agent (hereinafter, referred to as a surface cross-linking agent), and is subjected to surface cross-linking.
The crosslink density near the surface of the polymer can be higher than that inside. Thereby, a water-absorbing agent having excellent absorption characteristics can be obtained.

The above polymer can be reacted with a crosslinking agent without adjusting its water content. However, in order to maximize the absorption characteristics of the final product under high pressure, the polymer is dried. Preferably, after adjusting the water content to 10% by weight or less, pulverization is performed as necessary, and after adjusting to a desired particle size, a crosslinking agent is preferably added and reacted.

The method for drying the polymer is not particularly limited, and various conventionally known methods such as hot-air drying, thin-film drying using a drum dryer, reduced-pressure drying, fluidized-bed drying, and freeze-drying can be used. Drying methods can be used. In this case, the drying temperature of the polymer is not particularly limited, but may be set to about 80 ° C to 230 ° C. Further, the pulverizing method is not particularly limited, for example, a method of pulverizing using a hammer type pulverizer, a roll type pulverizer, or a jet stream type pulverizer, etc.
Various conventionally known pulverizing methods can be used.

The polymer as a water-absorbing agent precursor thus obtained is a primary particle or a granulated particle, and may be irregularly crushed, spherical, irregularly granular, rod-like, substantially spherical, flat, etc. And the water content is preferably 10% by weight or less, more preferably 5% by weight or less. The average particle size of the polymer particles obtained by pulverizing and classifying the polymer after drying is 200 μm to 600 μm, more preferably the ratio of particles having a particle size of 150 μm or less is 10% by weight or less, and further preferably 150 μm or less. Is 5% by weight or less.

The surface cross-linking agent is not particularly limited as long as it is a compound capable of reacting with the functional group of the polymer. As the surface crosslinking agent, specifically, for example, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, dipropylene glycol,
2,2,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerin, polyglycerin, 2-butene-1,4-diol, 1,4-butanediol, 1,5-pentanediol, 1,6 -Polyvalent such as hexanediol, 1,2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethyleneoxypropylene block copolymer, pentaerythritol and sorbitol Alcohol compounds: ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, polypropylene glycol diglycidyl ether, Polyhydric epoxy compounds such as ricidol; polyamine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyallylamine and polyethyleneimine; polyhydric amine compounds such as 2,4-tolylenediisocyanate, hexamethylenediisocyanate Polyvalent isocyanate compound; polyvalent oxazoline compound such as 1,2-ethylenebisoxazoline; 1,3-dioxolane
-2-one, 4-methyl-1,3-dioxolan-2-one, 4,5-
Dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-
1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-
2-one, 1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxan-2-one, 1,3-dioxopane Alkylene carbonates such as 2-one; epichlorohydrin, epibromohydrin, α-
Haloepoxy compound such as methyl epichlorohydrin; γ
Silane coupling agents such as aminopropyltrimethoxysilane; and polyvalent metals such as hydroxides and chlorides such as zinc, calcium, magnesium, aluminum, iron and zirconium, but are not particularly limited. .

These surface cross-linking agents may be used alone, or two or more of them may be used as appropriate. Among these surface crosslinking agents, the solubility parameter (SP
Surface cross-linking agent comprising a combination of a first surface cross-linking agent and a second surface cross-linking agent (US Pat. No. 5,422,4
No. 05) is preferred because a water-absorbing agent having particularly excellent absorption capacity under high pressure can be obtained. still,
The above-mentioned solubility parameter is a value generally used as a factor indicating the polarity of a compound. In the present invention, for the above-mentioned solubility parameter, Polymer Handbook, 3rd edition (issued by WILEY INTERSCIENCE), page 527 to
Solvent solubility parameter δ (cal
/ cm ³ ) ^1/2 value shall be applied. Also, regarding the solubility parameter of the solvent not described on the above page,
Sm described on page 524 of the polymer handbook
A value derived by substituting Hoy's cohesive energy constant described in page 525 into the all equation is applied.

As the first surface cross-linking agent, a solubility parameter capable of reacting with the functional group of the polymer and having a solubility parameter of 12.5 (c
al / cm ³ ) ^1/2 or more compounds are preferred, and 13.0 (cal / cm ³ ) ^1/2
The above compounds are more preferred. Specific examples of the first surface cross-linking agent include, for example, ethylene glycol, propylene glycol, glycerin, pentaerythritol, sorbitol, ethylene carbonate (1,3-dioxolan-2-one), propylene carbonate (4-methyl
-1,3-dioxolan-2-one) and the like, but are not limited to these compounds. One of these first surface cross-linking agents may be used alone, or two or more of them may be appropriately used in combination.

The second surface cross-linking agent has a solubility parameter capable of reacting with the functional group of the polymer.
Compounds less than 12.5 (cal / cm ³ ) ^1/2 are preferred, and 9.5 (cal / cm 3
Compounds in the range of ³ ) ^{1/2 to} 12.0 (cal / cm ³ ) ^1/2 are more preferred. As the second surface cross-linking agent, specifically, for example, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,3-butanediol,
1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,5-hexanediol, trimethylolpropane, ethylene glycol diglycidyl ether,
Examples include polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether, but are not limited to these compounds. One of these second surface cross-linking agents may be used alone, or two or more of them may be used as a mixture.

The amount of the surface cross-linking agent used, that is, the total amount of the first surface cross-linking agent and the second surface cross-linking agent depends on the type of the cross-linking agent to be used and the combination thereof, but is finally obtained. 0.001 based on 100 parts by weight of solid content of water absorbing agent
Parts by weight to 10 parts by weight, preferably 0.01 to 10 parts by weight.
More preferably, it is in the range of 5 parts by weight to 5 parts by weight. If the amount of the surface cross-linking agent used is within the above range, the cross-linking density in the vicinity of the surface of the water-absorbing agent can be made higher than that of the inside, whereby the absorption characteristics under pressure can be obtained regardless of the magnitude of the load. A water-absorbing agent excellent in water resistance. If the amount of the cross-linking agent is less than 0.001 part by weight, the effect of improving the absorption characteristics under pressure may not be sufficiently obtained. When the amount of the crosslinking agent exceeds 10 parts by weight, the added crosslinking agent is not used efficiently, which is not only uneconomical, but also forms an optimal crosslinking structure in the water-absorbing agent. Is liable to be excessive, and the absorption capacity may be excessively lowered, which is not preferable.

When mixing the above polymer and the surface cross-linking agent, at or after mixing, if necessary, water, steam, or an aqueous liquid comprising water and a hydrophilic organic solvent may be added. Is also good. At this time, when the surface cross-linking agent is a compound that reacts with a polymer by a covalent bond, such as a polyhydric alcohol compound, a polyhydric epoxy compound, or an alkylene carbonate, water, steam, or water and a hydrophilic organic solvent are used as the solvent. The addition of an aqueous liquid or the like is preferred because the absorption characteristics under pressure may be greatly improved.

The hydrophilic organic solvent is not particularly limited, but specific examples thereof include methyl alcohol, ethyl alcohol, n-propyl alcohol,
lower alcohols such as o-propyl alcohol, n-butyl alcohol, iso-butyl alcohol, and t-butyl alcohol; ketones such as acetone; ethers such as dioxane, alkoxy (poly) ethylene glycol, and tetrahydrofuran; Amides such as dimethylformamide;
And sulfoxides such as dimethyl sulfoxide.

The amount of water used in this case depends on the type and particle size of the polymer used, but is not more than 10 parts by weight, preferably 1 part by weight, based on 100 parts by weight of the solid content of the polymer. ~ 5
It is within the range of parts by weight. The amount of the hydrophilic organic solvent used depends on the type and particle size of the polymer used, but is not more than 10 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the solid content of the polymer. It is within the range of parts by weight.

In mixing the above polymer and the surface crosslinking agent, for example, after dispersing the polymer in the above aqueous liquid,
The surface cross-linking agent may be mixed, or the surface cross-linking agent dissolved in water or an aqueous liquid may be directly sprayed or dropped on the polymer and mixed. In the case of mixing using water, fine particles insoluble in water, a surfactant, various organic acids and inorganic acids, and the like may coexist.

The mixing device used for mixing the polymer and the surface cross-linking agent preferably has a large mixing force in order to uniformly and surely mix the two.
Examples of the mixing device include a cylindrical mixer, a double-walled conical mixer, a V-shaped mixer, a ribbon-type mixer, a screw-type mixer, a fluid-type furnace rotary desk-type mixer,
An air-flow type mixer, a double-arm type kneader, an internal mixer, a pulverization type kneader, a rotary mixer, a screw type extruder and the like are preferable.

Although the detailed reason is not clear, the polymer having a specific neutralization index according to the present invention has much more uniform mixing with the surface cross-linking agent as compared with the conventional post-neutralization polymer. Are better.

In the present invention, after mixing the above polymer and a surface cross-linking agent, a heat treatment is carried out, if necessary, depending on the type of the cross-linking agent to cross-link the vicinity of the surface of the polymer. The treatment temperature of the heat treatment depends on the surface crosslinking agent used,
The temperature is preferably 80 ° C or higher, more preferably in the range of 100 ° C to 230 ° C, and particularly preferably in the range of 160 ° C to 220 ° C. When the heat treatment temperature is lower than 80 ° C., the heat treatment takes time, not only causes a decrease in productivity, but also does not form a uniform cross-linked structure, and the absorption characteristics under pressure, which is the object of the present invention. It may not be possible to obtain a water-absorbing agent having a high water absorption.

The above heat treatment can be carried out using a usual dryer or heating furnace. Examples of the dryer include a groove-type mixing dryer, a rotary dryer, a desk dryer, a fluidized-bed dryer, a flash dryer, and an infrared dryer. The above heat treatment time is preferably 1 minute to 120 minutes, more preferably 5 minutes to 60 minutes, depending on the type of heat treatment apparatus such as a dryer and a heating furnace used for the heat treatment.

The water absorbing agent obtained by the above production method is
The surface of the polymer particles is composed of a plurality of water-absorbing agent particles that are cross-linked, because the cross-linking of the surface of the water-absorbing agent particles is uniformly formed, not only high absorption capacity under no pressure, but also under pressure Absorption characteristics are improved, and even under a high pressure of 50 g / cm ² , physiological saline is 20 g / g or more, preferably
It exhibits an excellent absorption capacity of 23 g / g or more, more preferably 25 g / g or more, particularly preferably 27 g / g or more, and most preferably 30 g / g or more. The water-absorbing agent obtained by the above-mentioned production method has a water-soluble component content of 10% by weight or less, preferably 5% by weight or less.

As described above, in order to obtain a water-absorbing agent having a high absorption capacity under no pressure and under high pressure and a reduced amount of water-soluble components as compared with the conventional one, it is necessary to carry out post-neutralization. is there. In the present invention, the ideal lower limit of the neutralization index is 0. However, in order to set the neutralization index of the polymer obtained through the post-neutralization step to 0, for example, a large-scale mixing device is required, or ultra-high-speed mixing that places a large load on the product is required. As a result, the cost may be increased, and inconveniences such as breakage of the product may be caused. Therefore, the neutralization index is set to 0
Considering the effect corresponding to the disadvantages caused by the above, the lower limit of the neutralization index of the obtained water-absorbing agent is usually 1 in order to achieve the object of the present application. Since the neutralized state is maintained after the crosslinking reaction, the neutralization index of the water-absorbing agent as the final product is the same as that of the polymer particles at the time of the crosslinking reaction. Therefore, the obtained water-absorbing agent has a first neutralization index of 1 or more and 10 or less, preferably 0 or less.
Not less than 10 and / or the second neutralization index is not less than 1 and 30
Or less, preferably 0 or more and 30 or less, and 50 g / cm
Absorption capacity of physiological saline under load of ² is 20 g / g or more.

The neutralization index of a water-absorbing agent obtained by polymerizing an acid group-containing monomer previously neutralized to a desired neutralization ratio is such that the acid group-containing monomer as a raw material is already in a desired degree. Since it has a neutralization rate, both the first neutralization index and the second neutralization index become zero. However, when an acid group-containing monomer that has been previously neutralized to a desired neutralization ratio is polymerized, it is difficult to obtain a water-absorbing agent having a reduced water-soluble component.

Therefore, in order to stably obtain a water-absorbing agent having a reduced water-soluble component and a high absorption capacity under high pressure, it is necessary to carry out post-neutralization as described above.
It is necessary to control the neutralization rate of the polymer obtained by neutralizing the hydrogel polymer as a raw material at the particle level.

The water-absorbing agent according to the present invention has a high absorption capacity under no pressure and under high pressure, and absorbs and transfers liquid into the water-absorbing agent under any use condition regardless of under no pressure or under pressure. And a high liquid absorption space can be obtained even under high pressure conditions.
Therefore, the water-absorbing agent can be preferably used for a long time as a water-absorbing agent for sanitary articles or the like by being combined with a support structure made of a hydrophilic fiber material such as paper or ground pulp.

Further, a 100-fold swelled gel obtained by swelling the water-absorbing agent obtained by the present invention with water to 100 times its own weight,
The amount of change in pH between 5 minutes and 120 minutes after the formation of the 00-fold swelling gel is extremely small at 0.2 or less. That is, 100
After forming the double swelling gel, the pH of the 100-fold swelling gel after 5 minutes has passed is D ₁ , and the pH of the 100-fold swelling gel after 120 minutes has passed
Assuming that H is D ₂ , the following expression is satisfied: D ₁ −D ₂ ≦ | 0.2 | For this reason, sanitary articles using the water-absorbing agent have a low residual amount of alkali or acid used for neutralization, have excellent pH stability even when absorbing an aqueous solution such as a body fluid, and are safer than conventional ones. Have been improved.

As described above, according to the method for producing a water absorbing agent of the present invention, a hydrogel polymer obtained by polymerizing a monomer component containing an acid group-containing monomer (salt) is neutralized. By controlling the neutralization rate of the polymer particles derived from the obtained polymer to each of the allowable neutralization rates, the absorption capacity under no pressure and under high pressure (load) is high, and It is possible to stably provide a water-absorbing agent in which the amount of the water-soluble component is reduced as compared with the related art and the pH of the swollen gel is small. When a water-absorbing agent is produced without controlling the neutralization rate of the polymer particles, it is difficult to stably obtain a water-absorbing agent having excellent water-absorbing properties. Further, when the neutralization rate of the water-absorbing agent particles constituting the obtained water-absorbing agent is not controlled, when the water-absorbing agent is swollen with an aqueous liquid to form a swollen gel, the water-absorbing agent remains in the water-absorbing agent. Due to the acid or alkali used for the neutralization, the neutralization gradually progresses in the gel, which causes a problem of lack of safety and pH stability. Therefore, also from this, the water absorbing agent manufactured by the above manufacturing method can be safely used for a long time as a water absorbing agent for sanitary goods and the like.

When controlling the neutralization rate of the polymer particles, measuring (confirming) the neutralization index of the aggregate of the polymer particles means that the water-absorbing agent having excellent water-absorbing properties can be stabilized. This serves as an indication of the completion of neutralization of the hydrogel polymer to be obtained, and the hydrogel polymer can be uniformly neutralized at a particle level in a shorter time. As a result, the above-mentioned water-absorbing agent having excellent water-absorbing properties can be stably obtained in a shorter time.

Therefore, when obtaining the water-absorbing agent of the present invention, it is preferable to carry out a crosslinking step after confirming that the neutralization index of the polymer particles has become a predetermined value or less. However, as described above, the neutralization index can be used as a measure for ending the neutralization of the hydrogel polymer. For this reason, for example, at the time of the first production of the water-absorbing agent, a condition that satisfies the above-described neutralization index is confirmed, and neutralization is performed according to the condition. Can be omitted. That is, according to the present invention, the above-mentioned aggregate of polymer particles is neutralized so that the neutralization index is equal to or less than a predetermined value, whereby the water-absorbing agent particles constituting the water-absorbing agent are each allowed neutralization. It is possible to stably obtain a water-absorbing agent which is controlled so as to have an excellent water-absorbing property.

The water-absorbing agent of the present invention can be used, for example, in a water-absorbing article such as a disposable diaper or sanitary napkin obtained by compounding with a fibrous material, the ratio of the water-absorbing agent to the sum of the fibrous material such as pulp and the like. Even when used under high concentration conditions such as 50% by weight or more, the capillaries under load are not caused. Therefore, the use of the water-absorbing agent makes it possible to provide an absorbent body and a water-absorbent article which are excellent in diffusibility over a long period of time and have less leakage. As described above, the water-absorbing agent according to the present invention can efficiently exhibit its water-absorbing ability even when used in a thin absorber containing the water-absorbing agent at a high concentration, so that a large amount of the water-absorbing agent is used. In addition, it can be suitably used for an absorbent body in a sanitary article having a reduced thickness.

[0121]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited thereto. In addition, various properties of the water absorbing agent were measured by the following methods.

(A) Absorbency under normal pressure (under no load) 0.2 g of a water-absorbing agent was uniformly placed in a non-woven bag (60 mm × 60 mm), and placed in a saline solution (0.9% by weight aqueous sodium chloride solution) at room temperature. And soaked. After 60 minutes, the bag was lifted up, drained with a centrifuge at 250 G for 3 minutes, and then the weight W ₁ (g) of the bag was measured. The same operation was performed without using a water absorbing agent, and the weight W ₀ (g) at that time was measured. Then, from these weights W ₁ · W ₀ , the following formula: absorption capacity under normal pressure (g / g) = (weight W ₁ (g) −weight W ₀ (g)) / weight (g) −1 of water absorbing agent The absorption capacity under normal pressure (g / g) was calculated according to the following.

(B) Absorption capacity under pressure (under load) First, a measuring apparatus used for measuring the absorption capacity under pressure will be briefly described below with reference to FIG.

As shown in FIG. 3, the measuring device is a balance 1
And a container 2 having a predetermined capacity mounted on the balance 1, an outside air suction pipe 3, a conduit 4, a glass filter 6, and a measuring unit 5 mounted on the glass filter 6. I have.

The container 2 has an opening 2a at the top.
The outside air suction pipe 3 is fitted into the opening 2a, and the conduit 4 is attached to the opening 2b. In addition, in the container 2,
A predetermined amount of physiological saline 12 is contained.

The lower end of the outside air suction pipe 3 is
Submerged in physiological saline 12. The outside air suction pipe 3
Is provided to keep the pressure in the container 2 at substantially normal pressure (atmospheric pressure).

The above glass filter 6 is formed to have a diameter of 70 mm. The container 2 and the glass filter 6 communicate with each other by a conduit 4 made of a silicone resin. Further, the position and the height of the glass filter 6 with respect to the container 2 are kept constant. Further, the glass filter 6 is fixed such that the upper surface thereof is at a position slightly higher than the lower end surface 3 a of the outside air suction pipe 3.

The measuring section 5 includes a filter paper 7 and a support cylinder 9.
And a wire mesh 10 attached to the bottom of the support cylinder 9, and a weight 11. In the measuring section 5, the filter paper 7 and the support cylinder 9 (that is, the wire mesh 10) are placed on the glass filter 6 in this order, and the weight 11 is placed inside the support cylinder 9, that is, on the wire mesh 10. Has become. The support cylinder 9 is formed to have an inner diameter of 60 mm, and the wire mesh 10 is made of stainless steel, and is formed to have a mesh size of 400 (mesh size 38 μm). Then, a predetermined amount of the water-absorbing agent 15 is evenly spread on the wire mesh 10. The weight 11 can uniformly apply a load to the wire netting 10, that is, the water absorbing agent 15.

The absorption capacity under pressure was measured using the measuring apparatus having the above-mentioned structure. The measuring method will be described below.

First, a predetermined amount of physiological saline 12 is placed in the container 2.
, And a predetermined preparation operation such as fitting the outside air suction pipe 3 into the container 2 was performed. Next, the filter paper 7 was placed on the glass filter 6. On the other hand, in parallel with this placing operation,
0.9 g of the water-absorbing agent 15 was evenly spread on the inside of the support cylinder 9, that is, on the wire mesh 10, and the weight 11 was placed on the water-absorbing agent 15.

Next, the wire mesh 10, that is,
The support cylinder 9 on which the water absorbing agent 15 and the weight 11 are placed
Was placed such that the center part thereof coincided with the center part of the glass filter 6.

Then, the weight W ₂ (g) of the physiological saline 12 absorbed by the water absorbing agent 15 was measured with the balance 1 over a period of 60 minutes after the support cylinder 9 was placed on the filter paper 7. It was determined from the value.

Then, based on the weight W ₂ (g) and the weight (0.9 g) of the water-absorbing agent 15, the absorption capacity under pressure (g / g) = weight W ₂ (g) / weight of the water-absorbing agent According to the weight (g), the absorption capacity (g / g) 60 minutes after the start of water absorption under pressure was calculated. For the measurement of absorption capacity under low pressure, a weight 11 having a load of 20 g / cm ² was used.
A weight 11 having a load of 50 g / cm ² was used for measuring the absorption capacity under high pressure.

(C) Amount of Water-Soluble Components 0.5 g of a water-absorbing agent is dispersed in 1000 g of deionized water.
After stirring for 16 hours, the mixture was filtered with filter paper. Next, 50 g of the obtained filtrate was placed in a 100 ml beaker, and 1 ml of a 0.1 N aqueous sodium hydroxide solution, 10 ml of an aqueous N / 200 methyl glycol chitosan solution, and 4 drops of a 0.1% toluidine blue aqueous solution were added to the filtrate. Thereafter, the amount of the water-soluble polymer component in the beaker was manually determined using an N / 400 aqueous solution of potassium polyvinyl sulfate. Then, the time when the color of the solution changed from blue to magenta was determined as the end point of the titration, and the titer A (ml) was determined. The same operation as above was performed using 50 g of deionized water instead of 50 g of the filtrate, and the titer B (ml) was determined as a blank. Then, from these titration amounts A and B and the molecular weight C of the water-absorbing agent, the water-soluble component amount (% by weight) is calculated according to the following formula: Water-soluble component amount (% by weight) = (BA) × 0.01 × C Calculated.

(D) pH change Pure water (temperature 23 ° C. ± 2 ° C.) was placed in a 250 ml beaker.
8.00 g was added, and the mixture was stirred with a magnetic stirrer using a rotor having a length of 40 mm. Then, under stirring, 2.000 g of a water-absorbing agent was added to the pure water at a time, and the pure water was all gelled uniformly, and allowed to stand until the rotor did not rotate. Immediately after stopping the rotor, the electrode of the pH meter (glass electrode type ion hydrogen concentration meter manufactured by Horiba, Ltd.) adjusted with the buffer solution was swollen in the beaker, that is, 100 times swelled by swelling to 100 times its own weight by water absorption. The gel was inserted almost in the center of the gel, and the pH value after 5 minutes (D ₁ ) and the pH value after 120 minutes (D
₂ ) and read. From these measured values, the pH change was calculated according to the following formula: pH change = (D ₁ ) − (D ₂ ).

In the present invention, a large change in pH is attributed to the fact that an unreacted alkali (eg, sodium hydroxide as a neutralizing agent) in the water-absorbing agent and a non-neutralized or low-neutralized polyacrylic acid (generally, Weak acid) and the powder
The fact that the gel is 100-fold swollen indicates that the neutralization gradually progresses with time in the gel even after swelling.
That is, the large change in pH in the present invention indicates that the water absorbing agent before swelling is still incompletely neutralized, and clearly indicates the residual acid or alkali used for the neutralization. The pH of the water-absorbing agent obtained from the previously neutralized monomer, which has not been subjected to post-neutralization, reaches an equilibrium value in approximately 5 minutes, and there is almost no change in pH over time thereafter.

Example 1 In a reactor in which a stainless steel double-armed kneader having a capacity of 10 L and having two sigma-type blades and a lid was attached,
Acrylic acid 720 g, N, N'-methylenebisacrylamide 3.08 g as internal crosslinking agent, deionized water 27 as solvent
18 g was charged to obtain a reaction solution. Next, the inside of the reactor was purged with nitrogen while maintaining the temperature of the reaction solution at 15 ° C. Next, 21.6 g of a 10% by weight aqueous solution of 2,2′-azobis (2-azinopropane) dihydrochloride as a polymerization initiator was added to the reaction solution while stirring the blade of the kneader, and a 1% by weight aqueous solution of L-ascorbic acid was added. 18.0 g and 3.5% peroxide solution 2
0.6 g was added to initiate the polymerization. At this time, the blade was stopped at the same time as the start of the polymerization, and the polymerization was carried out while appropriately raising the temperature of the jacket following the rise of the temperature of the reaction solution so that the temperature of the jacket was substantially equal to the temperature of the reaction solution. Then, after the temperature of the reaction solution reaches the maximum temperature,
Control the temperature of the jacket to 55
The reaction solution was maintained at a temperature of not less than ° C. and aged for 3 hours. After the completion of the reaction, the blade is rotated, and the obtained hydrogel crosslinked polymer is crushed into particles, thereby obtaining a particulate hydrogel crosslinked polymer (hereinafter referred to as a hydrogel polymer (A)). Described below).

Then, the hydrogel polymer (A) is kept at about 50 ° C. while further crushing by rotating the blade.
750 g of a 40% by weight aqueous sodium hydroxide solution as a neutralizing agent
Was added dropwise over 40 minutes and mixed. Thereafter, the blade was stopped and kept at 50 ° C. for 80 minutes. When a 1% by weight phenolphthalein-ethanol solution was added to the obtained polymer, reddish purple color of phenolphthalein was not observed. Further, an aqueous liquid of deionized water is added to the above polymer.
400 g was added, mixed, and kept at room temperature for 24 hours to complete the neutralization (neutralization rate: 75 mol%).

Thereafter, the polymer after neutralization (hereinafter referred to as polymer (A ₁ )) is dried with hot air at 50 ° C. for 16 hours, and the dried product is ground using a vibration mill and classified. And 1
Polymer particles (hereinafter, referred to as polymer particles (A ₁ )) as a water-absorbing agent precursor having a particle diameter of 50 μm to 850 μm were obtained. The water content of the polymer particles (A ₁ ) was 8% by weight.
Further, the neutralization index of the polymer particles (A ₁ ) was measured by the method described above.

Then, based on 100 parts by weight of the obtained polymer particles (A ₁ ), 0.5 parts by weight of glycerin as the first surface cross-linking agent, 0.05 parts by weight of ethylene glycol diglycidyl ether as the second surface cross-linking agent, and , Water 3 parts by weight and isopropyl alcohol 0.75 as a hydrophilic organic solvent
Parts of the aqueous liquid were added and mixed, and the resulting mixture was
A water absorbing agent was obtained by heating at 5 ° C. for 60 minutes. Various properties of this water absorbing agent were measured by the methods described above. The results are shown in Table 1 together with the neutralization index of the polymer particles (A ₁ ).

Example 2 The same reaction and operation as in Example 1 were performed to obtain an unneutralized hydrogel polymer (A). Thereafter, the hydrogel polymer (A) was kept at about 50 ° C. while further crushing, and 750 g of a 40% by weight aqueous sodium hydroxide solution was added dropwise over 40 minutes and mixed. Thereafter, the blade was stopped and kept at 50 ° C. for 80 minutes. When a 1% by weight phenolphthalein-ethanol solution was added to the obtained polymer, reddish purple color of phenolphthalein was not observed. Further, 400 g of deionized water was uniformly added to the above polymer, and the mixture was aged at room temperature for 5 days to complete the neutralization (neutralization ratio: 75 mol%).

Thereafter, the polymer after neutralization (hereinafter referred to as polymer (A ₂ )) was dried with hot air at 50 ° C. for 16 hours, and the dried product was ground using a vibration mill and classified. And 1
Polymer particles (hereinafter, referred to as polymer particles (A ₂ )) as a water-absorbing agent precursor having a particle diameter of 50 μm to 850 μm were obtained. The water content of the polymer particles (A ₂ ) was 5% by weight.
The neutralization index of the polymer particles (A ₂ ) was measured by the method described above.

Next, 1 part by weight of propylene glycol as a first surface cross-linking agent, 0.05 part by weight of ethylene glycol diglycidyl ether as a second surface cross-linking agent, based on 100 parts by weight of the obtained polymer particles (A ₂ ), An aqueous solution consisting of 3 parts by weight of water and 0.75 part of isopropyl alcohol was added and mixed, and the resulting mixture was heated at 175 ° C. for 40 minutes to obtain a water absorbing agent. Various properties of this water absorbing agent were measured by the methods described above. The results are shown in Table 1 together with the neutralization index of the polymer particles (A ₂ ).

Example 3 By performing the same reaction and operation as in Example 1, an unneutralized hydrogel polymer (A) was obtained. Thereafter, the hydrogel polymer (A) was kept at about 50 ° C. while further crushing, and 750 g of a 40% by weight aqueous sodium hydroxide solution was added dropwise over 40 minutes and mixed. After that, stop the blade, and
After holding for 0 minutes, a 1% by weight phenolphthalein-ethanol solution was added to the obtained polymer, and no reddish purple color of phenolphthalein was observed. Further, 400 g of deionized water was uniformly added to the above polymer, and the polymer was aged at room temperature for 12 hours to complete neutralization.

Thereafter, the polymer after neutralization (hereinafter referred to as polymer (A ₃ )) was dried with hot air at 50 ° C. for 16 hours.
The dried product was pulverized using a vibration mill and classified to obtain polymer particles as a water-absorbing agent precursor having a particle diameter of 150 μm to 850 μm (hereinafter, referred to as polymer particles (A ₃ )). . The water content of the polymer particles (A ₃ ) was 8% by weight. Further, the first neutralization index and the second neutralization index of the polymer particles (A ₃ ) were measured by the method described above.

Next, the obtained polymer particles (A ₃ ) 100
1 part by weight of propylene glycol as the first surface crosslinking agent, 0.05 parts by weight of ethylene glycol diglycidyl ether as the second surface crosslinking agent, and
An aqueous solution consisting of 3 parts by weight of water and 0.75 parts by weight of isopropyl alcohol was added and mixed, and the resulting mixture was heated at 175 ° C. for 40 minutes to obtain a water absorbing agent. Various properties of this water absorbing agent were measured by the methods described above. The results are shown in Table 1 together with the first neutralization index and the second neutralization index of the polymer particles (A ₃ ).

Example 4 The same reaction and operation as in Example 1 were performed to obtain an unneutralized hydrogel polymer (A). Thereafter, the hydrogel polymer (A) was kept at about 50 ° C. while further crushing, and 750 g of a 40% by weight aqueous sodium hydroxide solution was added dropwise over 40 minutes and mixed. Thereafter, the blade was stopped and kept at 50 ° C. for 80 minutes. When a 1% by weight phenolphthalein-ethanol solution was added to the obtained polymer, reddish purple color of phenolphthalein was not observed. Further, 200 g of deionized water was uniformly added to the above polymer, and the mixture was aged at room temperature for 12 hours to complete neutralization.

Thereafter, the polymer after neutralization (hereinafter referred to as polymer (A ₄ )) is dried with hot air at 50 ° C. for 16 hours, and the dried product is ground using a vibration mill and classified. And 1
Polymer particles (hereinafter, referred to as polymer particles (A ₄ )) as a water absorbing agent precursor having a particle diameter of 50 μm to 850 μm were obtained. The water content of the polymer particles (A ₄ ) was 7% by weight.
Further, the first neutralization index and the second neutralization index of the polymer particles (A ₄ ) were measured by the method described above.

Next, 1 part by weight of propylene glycol as a first surface cross-linking agent, 0.05 part by weight of ethylene glycol diglycidyl ether as a second surface cross-linking agent, based on 100 parts by weight of the obtained polymer particles (A ₄ ) An aqueous solution consisting of 3 parts by weight of water and 0.75 parts by weight of isopropyl alcohol was added and mixed.
Heat treatment was performed for a minute to obtain a water absorbing agent. Various properties of this water absorbing agent were measured by the methods described above. This result
The results are shown in Table 1 together with the first neutralization index and the second neutralization index of the polymer particles (A ₄ ).

Comparative Example 1 An unneutralized hydrogel polymer (A) was obtained by carrying out the same reaction and operation as in Example 1. Thereafter, the hydrogel polymer (A) was kept at about 50 ° C. while further crushing, and 750 g of a 40% by weight aqueous sodium hydroxide solution was added dropwise over 10 minutes and mixed. Thereafter, the blade was stopped and kept at 50 ° C. for 10 minutes. Then, when a 1% by weight phenolphthalein-ethanol solution was added to the obtained polymer, reddish purple color of phenolphthalein was clearly observed. Further, the polymer was aged at room temperature for 1 hour to neutralize it, thereby obtaining a polymer for comparison (hereinafter referred to as polymer (A ₅ )) (neutralization rate: 75 mol%).

Thereafter, the polymer (A ₅ ) was dried, pulverized and classified in the same manner as in Example 1 to obtain a polymer of 150 μm to 850 μm.
Polymer particles as a comparative water-absorbing agent precursor having a particle diameter of m (hereinafter, referred to as polymer particles (A ₅ )) were obtained. The water content of the polymer particles (A ₅ ) was 8% by weight. Further, the neutralization index of the polymer particles (A ₅ ) was measured by the method described above.

Next, using the polymer particles (A ₅ ),
A surface cross-linking treatment was performed in the same manner as in Example 1 to obtain a comparative water absorbing agent. Various properties of this water absorbing agent were measured by the methods described above. The results are shown in Table 1 together with the neutralization index of the polymer particles (A ₅ ).

Comparative Example 2 An unneutralized hydrogel polymer (A) was obtained by performing the same reaction and operation as in Example 1. Thereafter, the hydrogel polymer (A) was kept at about 50 ° C. while further crushing, and 750 g of a 40% by weight aqueous sodium hydroxide solution was added dropwise over 40 minutes and mixed. Thereafter, the blade was stopped and kept at 50 ° C. for 80 minutes. When a 1% by weight phenolphthalein-ethanol solution was added to the obtained polymer, reddish purple color of phenolphthalein was not observed. Further, the above polymer was neutralized by keeping the polymer at room temperature for 24 hours without adding deionized water (neutralization rate: 75 mol%). Thus, a polymer for comparison (hereinafter, referred to as polymer (A ₆ )) was obtained.

Thereafter, the polymer (A ₆ ) was dried, pulverized and classified in the same manner as in Example 1 to obtain a polymer of 150 μm to 850 μm.
Polymer particles as a comparative water absorbing agent precursor having a particle diameter of m (hereinafter, referred to as polymer particles (A ₆ )) were obtained. The water content of the polymer particles (A ₆ ) was 7% by weight. The neutralization index of the polymer particles (A ₆ ) was measured by the method described above.

Next, using the above polymer particles (A ₆ ),
A surface cross-linking treatment was performed in the same manner as in Example 1 to obtain a comparative water absorbing agent. Various properties of this water absorbing agent were measured by the methods described above. The results are shown in Table 1 together with the neutralization index of the polymer particles (A ₆ ).

Comparative Example 3 In a reactor similar to that of Example 1, 5367 g of a 33% by weight aqueous solution of a partially neutralized sodium acrylate having a neutralization ratio of 75 mol% was added.
A reaction solution prepared by dissolving 2.87 g of polyethylene glycol diacrylate as another monomer was charged. Next, the inside of the reactor was purged with nitrogen while maintaining the temperature of the reaction solution at 26 ° C. Next, 20% by weight as a polymerization initiator was added to the reaction solution while stirring the blade of the kneader.
12 g of an aqueous solution of sodium persulfate and 10 g of a 1% by weight aqueous solution of L-ascorbic acid were added, and polymerization was carried out for 60 minutes while crushing the gel. As a result, a particulate hydrogel crosslinked polymer (hereinafter, referred to as polymer (B)) was obtained. When a 1% by weight phenolphthalein-ethanol solution was added to the obtained polymer (B), reddish purple color of phenolphthalein was not confirmed.

Thereafter, the polymer (B) was dried, pulverized and classified in the same manner as in Example 1 to obtain a polymer having a particle size of 150 μm.
Polymer particles (B) as a comparative water absorbing agent precursor having a particle diameter of 850 μm were obtained. The water content of the polymer particles (B) was 6% by weight. Further, the neutralization index of the polymer particles (B) was measured by the method described above. In addition, each sodium polyacrylate crosslinked body having each neutralization ratio of 55 mol% or less was used as the comparative particles.

Next, using the polymer particles (B),
A surface cross-linking treatment was performed in the same manner as in Example 1 to obtain a comparative water absorbing agent. Various properties of this water absorbing agent were measured by the methods described above. The results are shown in Table 1 together with the neutralization index of the polymer particles (B).

[0159]

[Table 1]

From the results shown in Table 1, the water-absorbing agent using the polymer obtained in this example was not only under no pressure (normal pressure) but also under low pressure and high pressure. It can be seen that the amount of the water-soluble component was lower than that of the water-absorbing agent using the polymer obtained in Comparative Example.

Since the neutralization index of the polymer particles during the crosslinking reaction is also maintained in the final product, that is, the water-absorbing agent, the water-absorbing agent obtained in this example is different from the water-absorbing agent constituting the water-absorbing agent. It can be seen that the neutralization rate of the particles is controlled. In particular, the polymer particles obtained in Examples 1 and 2
And the number of polymer particles having a non-first allowable neutralization ratio in 200 polymer particles and a neutralization ratio of 95 mol% or more in 200 polymer particles. It can also be seen that the sum of the number of polymer particles having the ratio is also 10 or less. From the results shown in Table 1, the water-absorbing agent obtained in this example is uniformly neutralized at the particle level, so that it has a small change over time in pH during swelling and is excellent in safety. I understand.

[0162]

As described above, the water-absorbing agent according to the first aspect of the present invention is a water-containing gel polymer obtained by polymerizing a monomer component containing an acid group-containing unsaturated monomer (salt). A water-absorbing agent obtained by post-neutralization and comprising an aggregate of a plurality of surface-crosslinked water-absorbent particles, the average neutralization rate of the aggregate of the water-absorbent particles
Is defined as Z ₂ (mol%), and in the above 200 water absorbing agent particles,
Included, equation Z ₁ below> Z ₂ -20 absorbing agent particles having a low neutralization ratio than neutralization ratio Z ₁ satisfying (mol%)
The number of offspring is 10 or less, and the absorption capacity of physiological saline under a load of 50 g / cm ² is 20 g / g or more.

The water-absorbing agent according to the second aspect of the present invention is obtained from an aggregate of a plurality of surface-crosslinked water-absorbing agent particles as described above.
And the following relationship contained in the 200 water-absorbing agent particles:
Wherein Z _1> Z ₂ -20 absorbing agent particles having a low neutralization ratio than neutralization ratio Z ₁ satisfying (mol%)
The number of children is not less than 1 and not more than 10 .

[0164] water-absorbing agent according to claim 3 of the present invention, as described above, in claim 1 or 2 wherein the water-absorbing agent, the
Neutralization ratio Z ₁ is configured a neutralization ratio exceeds 55 mol%.

The water-absorbing agent according to claim 4 of the present invention is, as described above, a monomer component containing an acid group-containing unsaturated monomer (salt).
Is obtained by post-neutralizing the hydrogel polymer obtained by polymerizing
Consisting of an aggregate of a plurality of surface-crosslinked water-absorbing agent particles
A water-absorbing agent, contained in 200 of the water-absorbing agent particles,
Water-absorbing agent particles having a neutralization ratio of 30 mol% or less, and 95 mol%
The total number of water-absorbing agent particles having the above neutralization ratio is 30 or less
And a saline solution under a load of 50 g / cm ^2.
The configuration is such that the yield ratio is 20 g / g or more .

The water-absorbing agent according to the fifth aspect of the present invention is obtained from an aggregate of a plurality of surface-crosslinked water-absorbing agent particles as described above.
30% by mole or less contained in the 200 water-absorbing agent particles
Water-absorbing agent particles with the following neutralization rate and neutralization of 95 mol% or more
And the total number of water-absorbing agent particles having
This is the configuration below .

As described above, the water absorbing agent according to the sixth aspect of the present invention can be used in the water absorbing agent according to any one of the first to fifth aspects.
And the water-soluble component of the water-absorbing agent is 10% by weight or less .

As described above, the water-absorbing agent according to the seventh aspect of the present invention is the same as the water-absorbing agent according to any one of the first to sixth aspects.
And swell the water absorbing agent to 100 times its own weight with water.
100 minutes swelling gel after 5 minutes and 120 minutes
The amount of change in pH of the 100-fold swollen gel after the passage is 0.2
The configuration is as follows.

The water-absorbing agent according to claim 8 of the present invention comprises
Thus, the water-absorbing agent according to any one of claims 1 to 7,
The hydrated gel polymer has an internal crosslinking agent inside.
Wherein the internal crosslinking agent is non-crosslinked.
The configuration is an ester bond type internal cross-linking agent.

According to the above configuration, the water absorbing agent has a high absorption capacity under no pressure and under high pressure, a reduced amount of water-soluble components, and a small change in pH of the swollen gel. Can be provided stably. The water-absorbing agent has high safety and can effectively exhibit its water-absorbing ability even when used in a thin absorbent containing the water-absorbing agent in a high concentration. In addition, there is an effect that it can be suitably used for an absorber in a sanitary article having a reduced thickness.

The method for producing a water-absorbing agent according to the ninth aspect of the present invention contains an acid group-containing unsaturated monomer (salt) as described above.
Post-neutralize the hydrogel polymer obtained by polymerizing the monomer components
And the post-neutralized hydrogel polymer is subjected to the hydrogel.
With a cross-linking agent that can react with the functional group of the polymer
And crosslinking the surface.
In the step of post-neutralizing the hydrogel polymer,
After the above hydrogel polymer was neutralized, dried and pulverized
Assuming that the average neutralization rate of the aggregate of the polymer particles as the water absorbing agent precursor is Z ₂ (mol%), the polymer particles
Contained in 200 grain, the first neutralization index indicating the number of polymer particles having a low neutralization ratio than neutralization ratio Z ₁ satisfying the following relationship Z _1> Z ₂ -20 (mole%) But above 10
This is a configuration in which neutralization is performed after writing .

According to the method for producing a water-absorbing agent according to the tenth aspect of the present invention, as described above, the post-neutralization is performed when the first neutralization index is 5%. it is configured to perform so that less.

[0173] The method of claim 11, wherein the water-absorbing agent of the present invention, as described above, in the manufacturing method according to claim 9 or 10, wherein the water-absorbing agent, in which the neutralization rate Z ₁ exceeds 55 mole% The configuration is a sum rate.

The method for producing a water-absorbing agent according to the twelfth aspect of the present invention contains an acid group-containing unsaturated monomer (salt) as described above.
Post-neutralization of hydrogel polymer obtained by polymerizing
A step of, a post-neutralized hydrogel polymer, hydrous
Reaction with crosslinker that can react with functional group of gel polymer
And a step of cross-linking the surface.
In the step of post-neutralizing the hydrogel polymer,
After the above hydrogel polymer was neutralized, dried and pulverized
The number of polymer particles having a neutralization ratio of 30 mol% or less and the number of polymer particles having a neutralization ratio of 95 mol% or more contained in 200 polymer particles as a water absorbing agent precursor second neutralization index indicating the total number of the number of the upper so that 30 or less
This is a configuration in which neutralization is performed after writing .

According to the method for producing a water-absorbing agent according to the thirteenth aspect of the present invention, as described above, the post-neutralization and the second neutralization index of the water-absorbing agent according to the twelfth aspect are the same. it is configured to perform so that less.

The method for producing a water-absorbing agent according to the fourteenth aspect of the present invention is, as described above , the method for producing a water-absorbing agent according to any one of the ninth to thirteenth aspects.
The monomer (salt) is free acrylic acid.

The method for producing a water-absorbing agent according to claim 15 of the present invention is, as described above , the method for producing a water-absorbing agent according to any one of claims 9 to 14 , wherein the post-neutralization is Including
After mixing the water-gel polymer and the neutralizing agent, the aqueous liquid
This is a configuration performed by mixing .

As described above, the method for producing a water-absorbing agent according to claim 16 of the present invention relates to the method for producing a water-absorbing agent according to claim 15 with respect to 100 parts by weight of the hydrogel polymer.
The amount of the aqueous liquid used is in the range of 5 parts by weight to 100 parts by weight .

According to the above production method, the absorption capacity under no pressure and under high pressure is high, the amount of water-soluble components is reduced as compared with the conventional method, and the pH change of the swollen gel is small. This has the effect that the agent can be stably provided. Further, when producing the water-absorbing agent, the conditions satisfying the neutralization index of the present invention are checked in advance, and neutralization is performed in accordance with the conditions to obtain a water-absorbing agent excellent in each of the water-absorbing properties. It can be obtained efficiently in a shorter time.

The water-absorbent article according to claim 17 of the present invention
As described above, water absorption according to any one of claims 1 to 8.
Composition obtained by compounding an agent with a fibrous material.
You.

According to the above configuration, the water absorbing agent and the pulp
The ratio of the water-absorbing agent to the total with the fibrous material is 50% by weight or less.
Even when used under high concentration conditions such as above,
Without causing capillary blockage in
Excellent absorption over a long period of time with low leakage
The effect that an aqueous article can be provided is produced.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating a neutralization state at a particle level of a hydrogel polymer used as a raw material of a water-absorbing agent in the present invention, which is derived from a polymer obtained by neutralizing the hydrogel polymer. It is explanatory drawing shown by the number of the non-neutralization particles which have a non-first permissible neutralization rate contained in a particle.

FIG. 2 is an explanatory diagram illustrating a method of measuring a neutralization index according to the present invention.

FIG. 3 is a schematic cross-sectional view of a measuring device used for measuring absorption capacity under pressure, which is one of the properties exhibited by the water absorbing agent in the present invention.

FIG. 4 shows the state of neutralization of the conventional hydrogel polymer at the particle level, which is obtained by neutralizing the hydrogel polymer in a plurality of polymer particles derived from a polymer obtained by neutralizing the hydrogel polymer. It is explanatory drawing shown by the number of non-neutralizing particles which have an allowable neutralization rate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Polymer particle 21a Neutralized particle 21b Non-neutralized particle 22 Plastic plate 22a Opening 23 Cover glass 23 'Cover glass

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kinya Nagasago 992, Nishioki, Okihama-shi, Aboshi-ku, Himeji-shi, Hyogo Nippon Shokubai Co., Ltd. (56) References International Publication 94/20547 (WO, A1) (58) Survey Field (Int.Cl. ⁷ , DB name) C08F 8/00-8/50

Claims (17)

(57) [Claims] 1. A plurality of surface-crosslinked water-absorbing agent particles obtained by post-neutralizing a hydrogel polymer obtained by polymerizing a monomer component containing an acid group-containing unsaturated monomer (salt). Wherein the average neutralization ratio of the aggregate of the water-absorbing agent particles is Z ₂ (mol%).
Then, the following water-absorbing agent particles contained in 200 particles,
Relation Z _1> Z ₂ -20 absorbing agent particles having a low neutralization ratio than neutralization ratio Z ₁ satisfying (mol%)
A water-absorbing agent , wherein the number of particles is 10 or less and the absorption capacity of physiological saline under a load of 50 g / cm ² is 20 g / g or more. 2. An aggregate of a plurality of surface-crosslinked water absorbing agent particles.
Consisting of the following water-absorbing agent particles,
Relation Z _1> Z ₂ -20 absorbing agent particles having a low neutralization ratio than neutralization ratio Z ₁ satisfying (mol%)
Characterized in that the number of offspring is 1 or more and 10 or less
Water absorbing agent. 3. Neutralization wherein said neutralization ratio Z ₁ exceeds 55 mol%.
Water absorption according to claim 1 or 2,
Agent. 4. A monomer containing an acid group-containing unsaturated monomer (salt).
The post-neutralization of the hydrogel polymer obtained by polymerizing the components
From the aggregate of a plurality of water-absorbing agent particles
Water-absorbing agent which is contained in 200 particles of the water-absorbing agent,
Water-absorbing agent particles with a neutralization rate and a neutralization rate of 95 mol% or more
The total number of water-absorbing agent particles is 30 or less, and 50
g / cm ² physiological saline absorption capacity under load of 20 g / g
A water absorbing agent characterized by the above . 5. An aggregate of a plurality of surface-crosslinked water absorbing agent particles.
30 moles of the water-absorbing agent particles
% Of water-absorbing agent particles having a neutralization rate of not more than 95% by mole
The total number of water-absorbing agent particles having a neutralization ratio is 1 or more, 30
A water-absorbing agent, wherein the water-absorbing agent is not more than particles. 6. The water-absorbing agent having a water-soluble component of 10% by weight or less.
The method according to any one of claims 1 to 5, wherein
Water absorbing agent. 7. The water absorbing agent is swollen with water to 100 times its own weight.
5 minutes after the 100-fold swollen gel was formed
The change in pH of the 100-fold swollen gel after 0 minutes has passed
7. The method according to claim 1, wherein the value is 0.2 or less.
2. The water-absorbing agent according to claim 1. 8. The hydrogel polymer according to claim 1 , wherein
Having a cross-linking structure introduced by a cross-linking agent;
The agent is a non-ester bond type internal cross-linking agent.
The water-absorbing agent according to any one of claims 1 to 7. 9. A monomer containing an unsaturated monomer (salt) containing an acid group.
Post-neutralizing the hydrogel polymer obtained by polymerizing the components
And the post-neutralized hydrogel polymer is mixed with the hydrogel polymer.
Reaction with a cross-linking agent that can react with the functional group
Surface-crosslinking step, and the step of post-neutralizing the hydrogel polymer,
After neutralizing the hydrogel polymer, dry and pulverize it.
That, when the average neutralization ratio of the aggregate of the polymer particles as the water-absorbing agent precursor and Z ₂ (mol%), the polymer particles 200 grains
Contained in, the first neutralization index indicating the number of polymer particles having a low neutralization ratio than neutralization ratio Z ₁ satisfying the following relationship Z _1> Z ₂ -20 (mole%), Up to be 10 or less
A method for producing a water-absorbing agent, comprising performing neutralization after the description . 10. The post-neutralization, wherein the first neutralization index is 5
The method for producing a water-absorbing agent according to claim 9, wherein the method is performed as follows. 11. The method for producing a water-absorbing agent according to claim 9, wherein said neutralization ratio Z ₁ is a neutralization ratio exceeding 55 mol%. 12. A monomer containing an unsaturated monomer (salt) containing an acid group.
Post-neutralization of hydrogel polymer obtained by polymerizing body components
And the post-neutralized hydrogel polymer is converted to the hydrogel form.
Reacted with a crosslinking agent capable of reacting with the functional group of the polymer,
Surface cross-linking step.
In the step of post-neutralizing the hydrogel polymer,
After neutralizing the hydrogel polymer, dry and pulverize it.
And the number of polymer particles having a neutralization rate of 30 mol% or less contained in 200 polymer particles as a water absorbing agent precursor.
Second neutralization index, in after the so that 30 or less; total number of the number of polymer particles having a mol% neutralization ratio
A method for producing a water-absorbing agent, comprising summing . 13. The post-neutralization, wherein the second neutralization index is 20
The method for producing a water absorbing agent according to claim 12, wherein the method is performed as follows. 14. The process for producing a water-absorbing agent according to claim 9 , wherein said acid group-containing unsaturated monomer (salt) is free acrylic acid. 15. The post-neutralization is carried out with the hydrogel polymer.
After mixing with the neutralizing agent, further mixing the aqueous liquid
The method for producing a water-absorbing agent according to any one of claims 9 to 14 , wherein the method is performed. 16. A method according to claim 1, wherein the water-containing gel polymer is 100 parts by weight.
Range der of that amount of the aqueous solution 5 parts by weight to 100 by weight parts
The method of claim 15, wherein the water-absorbing agent, characterized in that that. 17. The water absorption according to claim 1,
Characteristically obtained by compounding an agent with a fibrous material
Absorbent article.